Hydro-climatic trends in the Abay/Upper Blue Nile basin,Ethiopia

Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay/Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann–Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations.Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar – typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.5 °C/decade, 0.3 °C/decade in rainy season (June–September), 0.6 °C/decade in small rainy season (March–May), and 0.6 °C/decade in dry season (October–February). Other stations in the Abay/Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use/land cover change and climate variability on streamflow of Abay/Blue Nile basin and its tributaries needs to be understood better.     

Dynamics in land cover and its effect on stream flow in the Chemoga watershed,Blue Nile basin,Ethiopia

The objective of this study was to analyse changes in stream flow patterns with reference to dynamics in land cover/use in a typical watershed, the Chemoga, in northwestern highland Ethiopia. The results show that, between 1960 and 1999, total annual stream flow decreased at a rate of 1 · 7 mm year⁻¹, whereas the annual rainfall decreased only at a rate of 0 · 29 mm year⁻¹. The decrease in the stream flow was more pronounced during the dry season (October to May), for which a statistically significant decline (0 · 6 mm year⁻¹) was observed while the corresponding rainfall showed no discernible trend. The wet season (June to September) rainfall and stream flow did not show any trends. Extreme low flows analysed at monthly and daily time steps reconfirmed that low flows declined with time, the changes being highly significant statistically. Between 1960 and 1999, the monthly rainfall and stream flow amounts of February (month of lowest long‐term mean flow) declined by 55% and 94% respectively. Similarly, minimum daily flows recorded during the three driest months (December to February) showed statistically highly significant declines over the same period. It declined from 0 · 6 m³ s⁻¹ to 0 · 2 m³ s⁻¹ in December, from 0 · 4 m³ s⁻¹ to 0 · 1 m³ s⁻¹ in January and from 0 · 4 m³ s⁻¹ to 0 · 02 m³ s⁻¹ in February (1 · 0 m³ s⁻¹ = 0 · 24 mm day⁻¹ in the Chemoga watershed). In contrast, extreme high flows analysed at monthly (for August) and daily (July to September) time steps did not reveal discernible trends. The observed adverse changes in the stream flow have partly resulted from changes in land cover/use and/or degradation of the watershed that involved destruction of natural vegetative covers, expansion of croplands, overgrazing and increased area under eucalypt plantations. The other contributory factor has been the increased dry‐season water abstraction to be expected from the increased human and livestock populations in the area. Given the significance of the stream flow as the only source of water to the local people, a set of measures aimed at reducing magnitudes of surface runoff generation and increasing groundwater recharge are required to sustain the water resource and maintain a balanced dry‐season flow in the watershed. Generally, an integrated watershed management approach, whereby the whole of the watershed can be holistically viewed and managed, would be desirable. Copyright © 2004 John Wiley & Sons, Ltd.     

Changes in water availability in the Upper Blue Nile basin under the representative concentration pathways scenario

Climatic and hydrological changes will likely be intensified in the Upper Blue Nile (UBN) basin by the effects of global warming. The extent of such effects for representative concentration pathways (RCP) climate scenarios is unknown. We evaluated projected changes in rainfall and evapotranspiration and related impacts on water availability in the UBN under the RCP4.5 scenario. We used dynamically downscaled outputs from six global circulation models (GCMs) with unprecedented spatial resolution for the UBN. Systematic errors of these outputs were corrected and followed by runoff modelling by the HBV (Hydrologiska ByrånsVattenbalansavdelning) model, which was successfully validated for 17 catchments. Results show that the UBN annual rainfall amount will change by ?2.8 to 2.7% with a likely increase in annual potential evapotranspiration (in 2041–2070) for the RCP4.5 scenario. These changes are season dependent and will result in a likely decline in streamflow and an increase in soil moisture deficit in the basin.     

Modeling the climatic effects of the land use/cover change in eastern China

This study aims to quantify the contribution of land use/cover change (LUCC) during the last three decades to climate change conditions in eastern China. The effects of farmland expansion in Northeast China, grassland degradation in Northwest China, and deforestation in South China were simulated using the Weather Research and Forecasting (WRF) model in addition to the latest actual land cover datasets. The simulated results show that when forestland is converted to farmland, the air temperature decreased owing to an increase in surface albedo in Northeast China. The climatic effect of grassland degradation on the Loess Plateau was insignificant because of the negligible difference in albedo between grassland and cropland. In South China, deforestation generally led to a decrease in temperature. Furthermore, the temperature decrease caused by the increase in albedo counteracted the warming effects of the evapotranspiration decrease, so the summer temperature change was not significant in South China. Excluding the effects of urbanization in the North China Plain, the LUCC effects across the entire region of East China presented an overall cooling trend. However, the variation in temperature scale and magnitude was less in summer than that in winter. This result is due mainly to the cooling caused by the increase in albedo offset partly by the increase in temperature caused by the decrease in evaporation in summer. Summer precipitation showed a trend of increasing–decreasing–increasing from southeast to northwest after LUCC, which was induced mainly by the decrease in surface roughness and cyclone circulations appearing northwest of Northeast China, in the middle of the Loess Plateau, and in Yunnan province at 700 hPa after forests were converted into farmland. All results will be instructive for understanding the influence of LUCC on regional climate and future land planning in practice.     

Effects of mid‐twenty‐first century climate and land cover change on the hydrology of the Puget Sound basin,Washington

The distributed hydrology–soil–vegetation model (DHSVM) was used to study the potential impacts of projected future land cover and climate change on the hydrology of the Puget Sound basin, Washington, in the mid‐twenty‐first century. A 60‐year climate model output, archived for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), was statistically downscaled and used as input to DHSVM. From the DHSVM output, we extracted multi‐decadal averages of seasonal streamflow, annual maximum flow, snow water equivalent (SWE), and evapotranspiration centred around 2030 and 2050. Future land cover was represented by a 2027 projection, which was extended to 2050, and DHSVM was run (with current climate) for these future land cover projections. In general, the climate change signal alone on sub‐basin streamflow was evidenced primarily through changes in the timing of winter and spring runoff, and slight increases in the annual runoff. Runoff changes in the uplands were attributable both to climate (increased winter precipitation, less snow) and land cover change (mostly reduced vegetation maturity). The most climatically sensitive parts of the uplands were in areas where the current winter precipitation is in the rain–snow transition zone. Changes in land cover were generally more important than climate change in the lowlands, where a substantial change to more urbanized land use and increased runoff was predicted. Both the annual total and seasonal distribution of freshwater flux to Puget Sound are more sensitive to climate change impacts than to land cover change, primarily because most of the runoff originates in the uplands. Both climate and land cover change slightly increase the annual freshwater flux to Puget Sound. Changes in the seasonal distribution of freshwater flux are mostly related to climate change, and consist of double‐digit increases in winter flows and decreases in summer and fall flows. Copyright © 2010 John Wiley & Sons, Ltd.     

On the ability of large-scale hydrological models to simulate land use and land cover change impacts in Amazonian basins

ABSTRACT

The MHD-INPE model was applied in the Ji-Parana Basin, a 30 000 km² catchment located in the southwest of the Amazon Basin which has lost more than 50% of its forest since the 1980s, to simulate land use and land cover change impacts on runoff generation process and how they are related to basin topography. Simulation results agree with observational studies in the sense that fast response processes are significant in sub-basins with steep slopes while in basins with gentle topography, the impacts are most visible in slow-response hydrological processes. On the other hand, the model is not able to capture the dependence of LUCC impacts on spatial scales. These discrepancies are probably associated with limitations in the spatial representation of heterogeneities within the model, which become more relevant at larger scales. We also tested the hypothesis that secondary forest growth should be able to compensate the decrease in evapotranspiration due to forest–cropland or forest–grassland conversion at a regional scale. Results showed that despite the small fraction of secondary forest estimated on the basin, the higher evapotranspiration efficiency of this type of forest counterbalances a large fraction of the LUCC impacts on evapotranspiration. This result suggests that enhanced transpiration due to secondary forest could explain, at least in part, the lack of clear LUCC signals in discharge series at larger scales.

EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR T. Wagener     

Hydrologic response to future land use change in the Upper Mississippi River Basin by the end of 21st century

This study demonstrates the spatial variation in hydrologic processes across the Upper Mississippi River Basin (UMRB) by the end of 21st century, by ingesting FOREcasting Scenarios (FORE‐SCE) of Land‐use Change projections into a physics‐based hydrologic model—Soil and Water Assessment Tool. The model is created for UMRB (440,000 km²), using the National Landcover Database of year 2001 and climate data of 1991–2010. Considering 1991–2010 as the baseline reference period, FORE‐SCE projections of year 2091 under three scenarios (A1B, A2, and B1 from the Intergovernmental Panel on Climate Change) are separately assimilated into the calibrated model, whereas climate input is kept the same as in the baseline. Modeling results suggest an increase of 0.5% and 3.5% in the average annual streamflow at the basin outlet (Grafton, Illinois) during 2081–2100, respectively, for A1B and A2, whereas for B1, streamflow would decrease by 1.5%. Under the “worst case” A2 scenario, 6% and 133% increase, respectively, in agricultural and urban areas with 30% depletion of forest and grassland would result into 70% increase in surface runoff, 20% decrease in soil moisture, and 4% decrease in evapotranspiration in certain parts of the basin. Conversion of cropland, forest, or grassland to perennial hay/pasture areas would lower surface runoff by 25% especially in the central region, whereas persistent forest cover in the northern region would cause up to 7% increase in evapotranspiration. The ecosystem in the lower half of UMRB is likely to become adverse, as dictated by a composite water–energy balance indicator. Future land use change extents and resultant hydrologic responses are found significantly different under A2, A1B, and B1 scenarios, which resonates the need for multi‐scenario ensemble assessments towards characterizing a probable future. The spatial variation of hydrologic processes as shown here helps to identify potential “hot spots,” giving ways to adopt more effective policy alternatives at regional level.     

Quantifying the impacts of climate change and land use/cover change on runoff in the lower Connecticut River Basin

Climate change and land use and cover change (LUCC) have had great impacts on watershed hydrological processes. Although previous studies have focused on quantitative assessment of the impacts of climate change and human activities on decreasing run‐off change, few studies have examined regions that have significant increasing run‐off due to both climate variability and land cover change. We show that annual run‐off had a significant increasing trend from 1956 to 2014 in the U.S. lower Connecticut River Basin. Abrupt change point years of annual run‐off for four subbasins are detected by nonparametric Mann–Kendall–Sneyers test and reconfirmed by the double mass curve. We then divide the study period into 2 subperiods at the abrupt change point year in the early 1970s for each subbasin. The Choudhury–Yang equation based on Budyko hypothesis was used to calculate precipitation and potential evapotranspiration, and landscape elasticities of run‐off. The results show that the difference in mean annual run‐off between 2 subperiods for each subbasin ranged from 102 to 165.6 mm. Climate variations were the primary drivers of increasing run‐off in this region. Quantitative contributions of precipitation and potential evapotranspiration in all subbasins are 106.5% and ?3.6% on average, respectively. However, LUCC contributed both positively and negatively to run‐off: ?18.6%, ?13.3%, and 10.1% and 9.9% for 4 subbasins. This may be attributed to historical LUCC occurring after the abrupt change point in each subbasin. Our results provide critical insight on the hydrological dynamics of north‐east tidal river systems to communities and policymakers engaged in water resources management in this region.     

An assessment of the geomorphodiversity and land use/cover change (LUCC) effects associated with landslides in Meghalaya,India

The Shillong Plateau in the Eastern Himalayas is exposed to high seismicity, neo-tectonic activity and orographic precipitation that aggravated landslides in the region by affecting hillslope processes. Landscape development is influenced by landslide phenomenon and depends upon geomorphic processes and geomorphodiversity (GmD). It is linked intimately with geomorphology, hydrology and soil type. This study uses a remote sensing and GIS-based approach to assess the spatial linkage between GmD and landslide distribution in Meghalaya (India). GmD index (GmDI) is developed using geological, morphometric and geomorphological parameters and analysed with landslide distribution. The landslide distribution considering land use/cover change (LUCC) is also examined. The result shows that the region with high-relief, valley and depression zone, mainly along the Dauki fault, have a high to a very high GmDI. About 61% of landslide localities are in zones of high GmDI, concentrated in the central and eastern parts of Meghalaya. Density analysis of the very high class (class 5) of GmD confirms the same. Most of these landslides occur in dense and light-vegetated landmasses. However, the LUCC analysis reveals a significant increase in the built area on steeper slopes (average expansion ratio of 2.30 for slopes >15°) between 2017 and 2022, indicating a rising threat of landslides in urban areas of Meghalaya. The study presents the importance of GmD in active tectonic regions with particular reference to landslide potential and recent LUCC. It can aid decision-makers in planning sustainable developments and risk mitigation strategies for landslide hazards and geoconservation.     

Attribution of changes in the water balance of a tropical catchment to land use change using the SWAT model

Changes in the water balance of the Samin catchment (277.9 km²) on Java, Indonesia, can be attributed to land use change using the Soil Water Assessment Tool model. A baseline‐altered method was used in which the simulation period 1990–2013 was divided into 4 equal periods to represent baseline conditions (1990–1995) and altered land use conditions (1996–2001, 2002–2007, and 2008–2013). Land use maps for 1994, 2000, 2006, and 2013 were acquired from satellite images. A Soil Water Assessment Tool model was calibrated for the baseline period and applied to the altered periods with and without land use change. Incorporating land use change resulted in a Nash–Sutcliffe efficiency of 0.7 compared to 0.6 when land use change is ignored. In addition, the model performance for simulations without land use change gradually decreased with time. Land use change appeared to be the important driver for changes in the water balance. The main land use changes during 1994–2013 are a decrease in forest area from 48.7% to 16.9%, an increase in agriculture area from 39.2% to 45.4%, and an increase in settlement area from 9.8% to 34.3%. For the catchment, this resulted in an increase of the runoff coefficient from 35.7% to 44.6% and a decrease in the ratio of evapotranspiration to rainfall from 60% to 54.8%. More pronounced changes can be observed for the ratio of surface runoff to stream flow (increase from 26.6% to 37.5%) and the ratio of base flow to stream flow (decrease from 40% to 31.1%), whereas changes in the ratio of lateral flow to stream flow were minor (decrease from 33.4% to 31.4%). At sub‐catchment level, the effect of land use changes on the water balance varied in different sub‐catchments depending on the scale of changes in forest and settlement area.     

Sensitivity of surface air temperature change to land use/cover types in China

Using CRU high resolution grid observational temperature and ERA40 reanalysis surface air temperature data during 1960–1999, we investigated the sensitivity of surface air temperature change to land use/cover types in China by subtracting the reanalysis from the observed surface air temperature (observation minus reanalysis, OMR). The results show that there is a stable and systemic impact of land use/cover types on surface air temperature. The surface warming of each land use/cover type reacted differently to global warming. The OMR trends of unused land (⩾0.17 °C/decade), mainly comprised by sandy land, Gobi and bare rock gravel land, are obviously larger than those of the other land use/cover types. The OMR over grassland, farmland and construction land shows a moderate decadal warmingabout 0.12°C/decade, 0.10°C/decade, 0.12°C/decade, respectively. Woodland areas do not show a significant warming trend (0.06°C/decade). The overall assessment indicates that the surface warming is larger for areas that are barren and anthropogenically developed. The better the vegetation cover, the smaller the OMR warming trend. Responses of surface air temperature to land use/cover types with similar physical and chemical properties and biological processes have no significant difference. The surface air temperature would not react significantly until the intensity of land cover changes reach a certain degree. Within the same land use/cover type, areas in eastern China with intensive human activities exhibit larger warming trend. The results provide observational evidence for modeling research on the impact of land use/cover change on regional climate. Thus, projecting further surface climate of China in regional scale should not only take greenhouse gas increase into account, but also consider the impact of land use/cover types and land cover change. Supported by National Basic Research Program of China (Grant No. 2005CB422006), National Natural Science Foundation of China (Grant Nos. 90202012, 40771206)     

Impacts of climate change and land use change on runoff of forest catchment in northeast China

Hydrological processes change from the impacts of climate variability and human activities. Runoff in the upper reaches of the Hun‐Taizi River basin, which is mainly covered by forests in northeast China, decreased from 1960 to 2006. The data used in this study were based on runoff records from six hydrological stations in the upper reaches of the Hun‐Taizi River basin. Nonparametric Mann–Kendall statistic was used to identify change trends and abrupt change points and consequently analyze the change characteristics in hydrological processes. The abrupt change in the annual runoff in most subcatchments appeared after 1975. Finally, the effects of climate change and land cover change on water resources were identified using regression analysis and a hydrology model. Results of the regression analysis suggest that the correlation coefficients between precipitation and runoff prior to the abrupt change were higher compared with those after the abrupt change. Moreover, using hydrology model analysis, the water yield was found to increase because of the decrease in forest land. Copyright © 2012 John Wiley & Sons, Ltd.     

Shift from transport limited to supply limited sediment concentrations with the progression of monsoon rains in the Upper Blue Nile Basin

Long‐term erosion monitoring data in the Ethiopian highlands are only available from the Soil Conservation Research Program (SCRP) watersheds including the Anjeni watershed. The 113 ha Anjeni watershed was established in 1984 and fanya juu terraces were installed in 1986. Runoff and erosion data are available from three different plot sizes and at the watershed outlet. The objective of this study was to investigate how erosion processes and sediment rating parameters vary with plot size and the progression of the rainy monsoon phase. We analyzed runoff and sediment loss data from 40 plots and the watershed outlet. The dataset included erosion data from 24 newly constructed plots (3 m length) during the rainy monsoon phase of 2012 and 2013, and 16 long‐term plots (with 12, 16, 22, and 24% slopes and 3, 15 and 30 m lengths) and the watershed outlet during the period between 1986 to 1990. Sediment concentration (C) was fitted to runoff (Q) using a power regression equation (C = aQ^b). Sediment concentration and yield increased with increasing plot length from 3 m to 15 m, but sediment yield decreased as plot length increased to 30 m.The coefficients (a and b) were affected by plot size and the progression of the rainy monsoon phase. As plot size increases, the a value increased, while the b value decreased. Greater a values were observed during the beginning of the monsoon phase, while values of b were greater towards the end of the monsoon phase. Overall findings suggest that erosion from cultivated fields is primarily controlled by transport limitations at the beginning of the monsoon phase, while towards the end of the monsoon phase, as surface covers emerge, sediment availability will be reduced, and thus sediment source would be a limitation. Copyright © 2016 John Wiley & Sons, Ltd.     

Natural flood management,land use and climate change trade-offs: the case of Tarland catchment,Scotland

A distributed hydrological model (WaSiM-ETH) was applied to a mesoscale catchment to investigate natural flood management as a nonstructural approach to tackle flood risks from climate change. Peak flows were modelled using climate projections (UKCP09) combined with afforestation-based land-use change options. A significant increase in peak flows was modelled from climate change. Afforestation could reduce some of the increased flow, with greatest benefit from coniferous afforestation, especially replacing lowland farmland. Nevertheless, large-scale woodland expansion was required to maintain peak flows similar to present and beneficial effects were significantly reduced for larger “winter-type” extreme floods. Afforestation was also modelled to increase low-flow risks. Land-use scenarios showed catchment-scale trade-offs across multiple objectives meant “optimal” flood risk solutions were unlikely, especially for afforestation replacing lowland farmland. Hence, combined structural/nonstructural measures may be required in such situations, with integrated catchment management to synergize multiple objectives.     

北方半干旱区土地利用/覆被变化对湖泊水质的影响:以岱海流域为例(2000-2018年)

土地利用/覆被变化对明晰气候变化和人类活动对湖泊水环境的影响有重要作用.以北方典型农牧交错的岱海流域为研究对象,基于遥感解译技术、马尔可夫转移矩阵、综合污染指数法等方法,对2000-2018年岱海流域土地利用/覆被和湖泊水质的变化进行分析,并结合冗余分析法和计量分析模型探究长时间序列尺度下土地利用/覆被变化对湖泊水质的...     

Effects of a century of land cover and climate change on the hydrology of the Puget Sound basin

The Puget Sound basin in northwestern Washington, USA has experienced substantial land cover and climate change over the last century. Using a spatially distributed hydrology model (the Distributed Hydrology‐Soil‐Vegetation Model, DHSVM) the concurrent effects of changing climate (primarily temperature) and land cover in the basin are deconvolved, based on land cover maps for 1883 and 2002, and gridded climate data for 1915–2006. It is found that land cover and temperature change effects on streamflow have occurred differently at high and low elevations. In the lowlands, land cover has occurred primarily as conversion of forest to urban or partially urban land use, and here the land cover signal dominates temperature change. In the uplands, both land cover and temperature change have played important roles. Temperature change is especially important at intermediate elevations (so‐called transient snow zone), where the winter snow line is most sensitive to temperature change—notwithstanding the effects of forest harvest over the same part of the basin. Model simulations show that current land cover results in higher fall, winter and early spring streamflow but lower summer flow; higher annual maximum flow and higher annual mean streamflow compared with pre‐development conditions, which is largely consistent with a trend analysis of model residuals. Land cover change effects in urban and partially urban basins have resulted in changes in annual flow, annual maximum flows, fall and summer flows. For the upland portion of the basin, shifts in the seasonal distribution of streamflows (higher spring flow and lower summer flow) are clearly related to rising temperatures, but annual streamflow has not changed much. Copyright © 2009 John Wiley & Sons, Ltd.     

Land use/land cover change and implications for ecosystems services in the Likangala River Catchment,Malawi

Likangala River catchment in Zomba District of Southern Malawi is important for water resources, agriculture and provides many ecosystem services. Provisioning ecosystem services accrued by the populations within the catchment include water, fish, medicinal plants and timber among others. In spite of its importance, the River catchment is under threat from anthropogenic activities and land use change. This paper studies land uses and land cover change in the catchment and how the changes have impacted on the ecosystem services. Landsat 5 and 8 images (1984, 1994, 2005 and 2013) were used to map land cover change and subsequent inventorying of provisioning ecosystem services. Participatory Geographic Information Systems and Focus group discussions were conducted to identify provisioning ecosystems services that communities benefit from the catchment and indicate these on the map.Post classification comparisons indicate that since 1984, there has been a decline in woodlands from 135.3 km² in 1984 to 15.5 km² in 2013 while urban areas increased from 9.8 km² to 23.8 km² in 2013. Communities indicated that provisioning ecosystems services such as forest products, wild animals and fruits and medicinal plants have been declining over the years. In addition, evidence of catchment degradation through waste disposal, illegal sand mining, deforestation and farming on marginal lands were observed. Population growth, urbanization and demand for agricultural lands have contributed to this land use and land cover change. The study suggests addressing catchment degradation through integrated method where an ecosystems approach is used. Thus, both the proximate and underlying driving factors of land-use and land cover change need to be addressed in order to sustainably reduce ecosystem degradation.     

Using standardized indicators to analyse dry/wet conditions and their application for monitoring drought/floods: a study in the Logone catchment,Lake Chad basin

The standardized precipitation index (SPI) and standardized streamflow index (SSI) were used to analyse dry/wet conditions in the Logone catchment over a 50-year period (1951–2000). The SPI analysis at different time scales showed several meteorological drought events ranging from moderate to extreme; and SSI analysis showed that wetter conditions prevailed in the catchment from 1950 to 1970 interspersed with a few hydrological drought events. Overall, the results indicate that both the Sudano and Sahelian zones are equally prone to droughts and floods. However, the Sudano zone is more sensitive to drier conditions, while the Sahelian zone is sensitive to wetter conditions. Correlation analysis between SPI and SSI at multiple time scales revealed that the catchment has a low response to rainfall at short time scales, though this progressively changed as the time scale increased, with strong correlations (≥0.70) observed after 12 months. Analysis using individual monthly series showed that the response time reduced to 3 months in October.     

Mediating stream baseflow response to climate change: The role of basin storage

Inter‐basin differences in streamflow response to changes in regional hydroclimatology may reflect variations in storage characteristics that control the retention and release of water inputs. These aspects of storage could mediate a basin's sensitivity to climate change. The hypothesis that temporal trends in stream baseflow exhibit a more muted reaction to changes in precipitation and evapotranspiration for basins with greater storage was tested on the Oak Ridges Moraine (ORM) in Southern Ontario, Canada. Long‐term (>25 years) baseflow trends for 16 basins were compared to corresponding trends in precipitation amount and type and in potential evapotranspiration as well as shorter trends in groundwater levels for monitoring wells on the ORM. Inter‐basin differences in storage properties were characterized using physiographic, hydrogeologic, land use/land cover, and streamflow metrics. The latter included the slope of the basin's flow duration curve and basin dynamic storage. Most basins showed temporal increases in baseflow, consistent with limited evidence of increases and decreases in regional precipitation and snowfall: precipitation ratio, respectively, and recent increases in groundwater recharge along the crest of the ORM. Baseflow trend magnitude was uncorrelated to basin physiographic, hydrogeologic, land use/land cover, or flow duration curve characteristics. However, it was positively related to a basin's dynamic storage, particularly for basins with limited coverage of open water and wetlands. The dynamic storage approach assumes that a basin behaves as a first‐order dynamical system, and extensive open water and wetland areas in a basin may invalidate this assumption. Previous work suggested that smaller dynamic storage was linked to greater damping of temporal variations in water inputs and reduced interannual variability in streamflow regime. Storage and release of water inputs to a basin may assist in mediating baseflow response to temporal changes in regional hydroclimatology and may partly account for inter‐basin differences in that response. Such storage characteristics should be considered when forecasting the impacts of climate change on regional streamflow.     

Simulated watershed responses to land cover changes using the Regional Hydro‐Ecological Simulation System

In this work, we used the Regional Hydro‐Ecological Simulation System (RHESSys) model to examine runoff sensitivity to land cover changes in a mountain environment. Two independent experiments were evaluated where we conducted simulations with multiple vegetation cover changes that include conversion to grass, no vegetation cover and deciduous/coniferous cover scenarios. The model experiments were performed at two hillslopes within the Weber River near Oakley, Utah watershed (USGS gauge # 10128500). Daily precipitation, air temperature and wind speed data as well as spatial data that include a digital elevation model with 30 m grid resolution, soil texture map and vegetation and land use maps were processed to drive RHESSys simulations. Observed runoff data at the watershed outlet were used for calibration and verification. Our runoff sensitivity results suggest that during winter, reduced leaf area index (LAI) decreases canopy interception resulting in increased snow accumulations and hence snow available for runoff during the early spring melt season. Increased LAI during the spring melt season tends to delay the snow melting process. This delay in snow melting process is due to reduced radiation beneath high LAI surfaces relative to low LAI surfaces. The model results suggest that annual runoff yield after removing deciduous vegetation is on average about 7% higher than with deciduous vegetation cover, while annual runoff yield after removing coniferous vegetation is on average as about 2% higher than that produced with coniferous vegetation cover. These simulations thus help quantify the sensitivity of water yield to vegetation change. Copyright © 2013 John Wiley & Sons, Ltd.