Records of hydrological change and environmental disasters in sediments from deep Lake Issyk-Kul

In the context of global warming, the mountainous areas of Central Asia are sensitive to climate and environmental changes and are highly vulnerable to natural disasters. Here, we use high-resolution lacustrine grain-size and geochemical records from Lake Issyk-Kul to infer hydrological changes, environmental events, and their driving factors in the western Tianshan Mountains of Central Asia over the last 350 years. The regional hydrological and environmental changes can be divided into three phases. In stage I (1674–1860 AD), the values of total organic carbon (TOC), total nitrogen (TN) and magnetic susceptibility (MS) were high, and the element contents changed indistinctively, suggesting that lake water levels were relatively stable. In Stage II (1860–2000 AD), the TOC and TN contents increased, the MS values decreased, and the grain size changed markedly, suggesting that water levels fluctuated dramatically. In Stage III (2000–2013 AD), the coarse particle and migratory element contents increased dramatically, indicating that regional rainfall and runoff increased and that the water level rose. Studies have also shown that the synchronous increases in sedimentary coarse particles, TOC and migratory elements indicate multiple flood events. Extreme floods have been frequent and intense in recent years, which indicates that the climate is generally warming, which is in good agreement with tree ring data, ice core records and other sediment records in alpine regions. Additionally, the lake sediments recorded a seismic event in approximately 1910 AD, which was consistent with historical documentation. Comparative analysis of records suggests that the Atlantic Multidecadal Oscillation is one of the dominant factors driving climate and hydrological changes in the study area. Climate change, combined with natural disasters (e.g., earthquakes) and anthropogenic activities, is generating extreme floods and variations in hydrological patterns in the mountain basin. These findings can provide crucial information about sedimentary physicochemical clues for tracking past hydrological and environmental conditions and contribute to a better understanding of hydrological processes and driving factors in the mountainous areas of Central Asia.     

The relative impacts of climate change and urbanization on the hydrological response of a Korean urban watershed

We assessed the relative hydrological impacts of climate change and urbanization using an integrated approach that links the statistical downscaling model (SDSM), the Hydrological Simulation Program—Fortran (HSPF) and the impervious cover model (ICM). A case study of the Anyangcheon watershed, a representative urban region in Korea, illustrates how the proposed framework can be used to analyse the impacts of climate change and urbanization on water quantity and quality. The evaluation criteria were measurements of low flow (99, 95, and 90 percentile flow), high flow (10, 5, and 1 percentile value), pollutant concentration (30, 10, and 1 percentile value), and the numbers of days required to satisfy the target water quantity and quality for a sensitive comparison of subtle impacts of variations in these measures. Nine scenarios, including three climate scenarios (present conditions, A1B, and A2) and three land use change scenarios, were analysed using the HSPF model. The impacts of climate change on low flow (34·1–59·8% increase) and high flow (29·1–37·1% increase) were found to be much greater than those on the biochemical oxygen demand (BOD) (3·8–10·0% decrease). On the other hand, the impacts of urbanization on water quality (19·0–44·6% increase) are more significant than those on high (1·0–4·4% increase) and low flow (11·4–25·6% decrease). Furthermore, low flows are more sensitive to urbanization than high flows. The number of days required to satisfy the target water quantity and quality can be a sensitive criterion to compare the subtle impacts of climate and urbanization on human society, especially as they are much more sensitive than low flow and pollutant concentration. Finally, urbanization has a potent impact on BOD while climate change has a high impact on flow rate. Therefore, the impacts of both climate change and urbanization must be included in watershed management and water resources planning for sustainable development. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling how vegetation cover affects climate change impacts on streamflow timing and magnitude in the snowmelt‐dominated upper Tuolumne Basin,Sierra Nevada

We investigated, through hydrologic modelling, the impact of the extent and density of canopy cover on streamflow timing and on the magnitude of peak and late summer flows in the upper Tuolumne basin (2600–4000 m) of the Sierra Nevada, California, under current and warmer temperatures. We used the Distributed Hydrology Soil Vegetation Model for the hydrologic modelling of the basin, assuming four vegetation scenarios: current forest (partial cover, 80% density), all forest (uniform coverage, 80% density), all barren (no forest) and thinned forest (partial cover, 40% density) for a medium‐high emissions scenario causing a 3.9 °C warming over a 100‐year period (2001–2100). Significant advances in streamflow timing, quantified as the centre of mass (COM) of over 1 month were projected for all vegetation scenarios. However, the COM advances faster with increased forest coverage. For example, when forest covered the entire area, the COM occurred on average 12 days earlier compared with the current forest coverage, with the rate of advance higher by about 0.06 days year^?1 over 100 years and with peak and late summer flows lower by about 20% and 27%, respectively. Examination of modelled changes in energy balance components at forested and barren sites as temperatures rise indicated that increases in net longwave radiation are higher in the forest case and have a higher contribution to melting earlier in the calendar year when shortwave radiation is a smaller fraction of the energy budget. These increases contributed to increased midwinter melt under the forest at temperatures above freezing, causing decreases in total accumulation and higher winter and early spring melt rates. These results highlight the importance of carefully considering the combined impacts of changing forest cover and climate on downstream water supply and mountain ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of lateral flow and spatial scaling on the simulation of semi‐arid urban land surfaces in an integrated hydrologic and land surface model

Understanding and representing hydrologic fluxes in the urban environment is challenging because of fine scale land cover heterogeneity and lack of coherent scaling relationships. Here, the impact of urban land cover heterogeneity, scale, and configuration on the hydrologic and surface energy budget (SEB) is assessed using an integrated, coupled land surface/hydrologic model at high spatial resolutions. Archetypes of urban land cover are simulated at varying resolutions using both the National Land Cover Database (NLCD; 30 m) and an ultra high‐resolution land cover dataset (0.6 m). The analysis shows that the impact of highly organized, yet heterogeneous, land cover typical of the urban domain can cause large variations in hydrologic and energy fluxes within areas of similar land cover. The lateral flow processes that occur within each simulation create variations in overland flow of up to ±200% and ±4% in evapotranspiration. The impact on the SEB is smaller and largely restricted to the wet season for our semi‐arid forcing scenarios. Finally, we find that this seasonal bias, predominantly caused by lateral flow, is displaced by a systematic diurnal bias at coarser resolutions caused by deficiencies in the method used for scaling of land surface and hydrologic parameters. As a result of this research, we have produced land surface parameters for the widely used NLCD urban land cover types. This work illustrates the impact of processes that remain unrepresented in traditional high‐resolutions land surface models and how they may affect results and uncertainty in modeling of local water resources and climate. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimating the effects of climate change on the intensification of monsoonal‐driven stream discharge in a Himalayan watershed

Understanding potential hydrologic influences to continued climate change in Himalayan watersheds is important for management of transnational water resources. This study estimates the climate change impacts on hydrologic processes of the Kali Gandaki watershed from central Himalayan region using the Soil and Water Assessment Tool. Daily predicted stream discharge of the basin for 1981–95 following calibration was accurate with Nash Sutcliffe Efficiency value >0.75. Sensitivity analysis of the hydrologic parameters showed the precipitation and temperature lapse rates as the most sensitive parameters to the stream discharge. To assess the influence of continued climate change on hydrologic processes, we modified the weather inputs for the model using average, minimum and maximum temperature, and precipitation changes for the Special Report on Emission Scenarios B1, A1B and A2 derived from 16 General Circulation Models for 2080s. Mean annual stream discharge was approximately 39% higher than current values for the maximum temperature and precipitation changes of the A2 scenario and 22% less for minimum changes of the same scenario. Stream discharge was projected to be changed by +9% during monsoon season and by ?6% during pre‐monsoon season. Snowfall and snow melt were projected to be 30% and 29%, respectively, less than the current average for the maximum temperature and precipitation changes of the A2 scenario. Future simulations showed potential increase in monsoonal stream discharge associated with projected higher precipitation which when coupled with enhanced summer glacier melt might influence the downstream water availability of the basin. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrology of Blue Lake in the Dinaric karst

The aim of this paper is to analyse hydrological measurements obtained from Blue Lake located near the town of Imotski (Croatia), during the period from 6 November 2009 at 10:26 h to 4 September 2010 at 03:26 h (7230 h or 302 days). The water depth, water temperature and electrical conductivity of the water were continuously measured during this period. The measurements were obtained with a CTD DIVER (Schlumberger Water Services). The instrument was fixed at the bottom of Blue Lake, which means that all the measured data refer to a single point of measurement. The data represent the first systematic and continuous monitoring of the hydrological parameters of this fascinating karst phenomenon. The hydrological analysis also involved daily rainfall data and daily mean air temperatures recorded at the nearby Imotski meteorological station. The rate of water level rise and fall and the hourly and daily average inflow and outflow into and from the lake were calculated using the available data. The analysis led to the conclusion that Blue Lake is mainly recharged by water coming from the karst aquifer, the dimensions and the characteristics of which have not yet been adequately studied. Copyright © 2013 John Wiley & Sons, Ltd.     

Measuring water availability with limited ground data: assessing the feasibility of an entirely remote‐sensing‐based hydrologic budget of the Rufiji Basin,Tanzania, using TRMM,GRACE, MODIS,SRB, and AIRS

This study explores the feasibility of an entirely satellite remote sensing (RS)‐based hydrologic budget model for a ground data‐constrained basin, the Rufiji basin in Tanzania, from the balance of runoff (Q), precipitation (P), storage change (ΔS), and evapotranspiration (ET). P was determined from the Tropical Rainfall Measuring Mission, ΔS from the Gravity Recovery and Climate Experiment, and ET from the Moderate Resolution Imaging Spectroradiometer, the surface radiation budget, and the Atmosphere Infrared Radiation Sounder. Q was estimated as a residual of the water balance and tested against measured Q for a sub‐basin of the Rufiji (the Usangu basin) where ground measurements were available (R² = 0.58, slope = 1.9, root mean square error = 29 mm/month, bias = 14%). We also tested a geographical information system (GIS)‐driven (ArcCN‐runoff) runoff model (R² = 0.64, slope = 0.43, root mean square error = 39 mm/month). We conducted an error propagation analysis from each of the model's hydrologic components (P, ET, and ΔS). We find that the RS‐based model amplitude is most sensitive to ET and slightly less so to P, whereas the model's seasonal trends are most sensitive to ?S. Although RS–GIS‐driven models are becoming increasingly used, our results indicate that long‐term water resource assessment policy and management may be more appropriate than ‘instantaneous’ or short‐term water resource assessment. However, our analyses help develop a series of tools and techniques to progress our understanding of RS–GIS in water resource management of data‐constrained basins at the level of a water resource manager. Copyright © 2012 John Wiley & Sons, Ltd.     

A ground motion prediction equation for JMA instrumental seismic intensity for shallow crustal earthquakes in active tectonic regimes

The JMA (Japan Meteorological Agency) seismic intensity scale has been used in Japan as a measure of earthquake ground shaking effects since 1949. It has traditionally been assessed after an earthquake based on the judgment of JMA officials. In 1996 the scale was revised as an instrumental seismic intensity measure (I_JMA) that could be used to rapidly assess the expected damage after an earthquake without having to conduct a survey. Since its revision, Japanese researchers have developed several ground motion prediction equations (GMPEs) for I_JMA using Japanese ground motion data. In this paper, we develop a new empirical GMPE for I_JMA based on the strong motion database and functional forms used to develop similar GMPEs for peak response parameters as part of the PEER (Pacific Earthquake Engineering Research Center) Next Generation Attenuation (NGA) project. We consider this relationship to be valid for shallow crustal earthquakes in active tectonic regimes for moment magnitudes ( M ) ranging from 5.0 up to 7.5–8.5 (depending on fault mechanism) and rupture distances ranging from 0 to 200 km. A comparison of this GMPE with relationships developed by Japanese researchers for crustal and shallow subduction earthquakes shows relatively good agreement among all of the relationships at M 7.0 but relatively poor agreement at small magnitudes. Our GMPE predicts the highest intensities at small magnitudes, which together with research on other ground motion parameters, indicates that it provides conservative or upwardly biased estimates of I_JMA for M <5.5. Copyright © 2010 John Wiley & Sons, Ltd.     

An Abrupt Increase in the Summer High Temperature Extreme Days across China in the mid-1990s

Based on the daily maximum surface air temperature records from an updated homogenized temperature dataset for 549 Chinese stations during 1960-2008,we reveal that there is an abrupt increase in the number of days with high temperature extremes (HTEs,an HTE day is defined when the maximum temperature exceeds the 95th percentile of the daily maximum temperature distributions) across China in the mid-1990s.Before this regime shift,the average number of HTE days is about 2.9 d yr 1 during the period from the 1970s to the early 1990s,while it rocketed to about 7.2 d yr 1 after the mid-1990s.We show that the significant HTE day increase occurs uniformly across the whole of China after the regime shift.The observational evidence raises the possibility that this change in HTE days is associated with global-scale warming as well as circulation adjustment.Possible causes for the abrupt change in the HTE days are discussed,and the circulation adjustment is suggested to play a crucial role in the increase in HTE days in this region.     

基于DEM的等流时法改进研究

提出等流时单元的概念,对基于DEM的等流时流域汇流方法进行了改进。此方法不需要绘制等流时线,也不要求流域净雨是均匀的,且各单元的汇流时间可以变动,直接由各单元的汇流时间就可以计算出流域出口的流量过程。同时提出改进方法的模块化编程方法,给出调用接口,经在研究区伊通河中下游较大流域上的试用表明,该程序具有可推广性。