区域蒸散发量的遥感模型方法研究

蒸散是水资源管理的一个重要参数。与传统的蒸散计算方法相比,利用遥感进行蒸散研究具有快速、准确、大区域尺度及地图可视化显示等特点。本文通过研究,提出了基于能量平衡方法遥感反演蒸散发的计算模型,指出了模型参数的求解方法,建立了基于MOD IS遥感数据的大区域蒸散发遥感反演技术方法。通过对石羊河流域进行试验,反演误差基本小于10%,并且具有进一步推广的技术前景。     

The effects of climate change on potential groundwater recharge in Great Britain

The predicted increase in mean global temperature due to climate change is expected to affect water availability and, in turn, cause both environmental and societal impacts. To understand the potential impact of climate change on future sustainable water resources, this paper outlines a methodology to quantify the effects of climate change on potential groundwater recharge (or hydrological excess water) for three locations in the north and south of Great Britain. Using results from a stochastic weather generator, actual evapotranspiration and potential groundwater recharge time‐series for the historic baseline 1961–1990 and for a future ‘high’ greenhouse gas emissions scenario for the 2020s, 2050s and 2080s time periods were simulated for Coltishall in East Anglia, Gatwick in southeast England and Paisley in west Scotland. Under the ‘high’ gas emissions scenario, results showed a decrease of 20% in potential groundwater recharge for Coltishall, 40% for Gatwick and 7% for Paisley by the end of this century. The persistence of dry periods is shown to increase for the three sites during the 2050s and 2080s. Gatwick presents the driest conditions, Coltishall the largest variability of wet and dry periods and Paisley little variability. For Paisley, the main effect of climate change is evident during the dry season (April–September), when the potential amount of hydrological excess water decreases by 88% during the 2080s. Overall, it is concluded that future climate may present a decrease in potential groundwater recharge that will increase stress on local and regional groundwater resources that are already under ecosystem and water supply pressures. Copyright © 2007 John Wiley & Sons, Ltd.     

A method for estimating soil moisture storage in regions under water stress and storage depletion: a case study of Hai River Basin,North China

Soil moisture is a consideration for soil conservation, agricultural production and climate modelling. This article presents a simple method for estimating soil moisture storage under water stress and storage depletion conditions. The method is driven by the common agro‐hydrologic variables of precipitation (PPT), irrigation (IRR) and evapotranspiration (ET). The proposed method is successfully tested for the 152 000 km² floodplain region of Hai River Basin using 48 consecutive months (2003–2006) of data. Soil moisture data from global land data assimilation system/Noah land surface model are validated with ground‐truth data from 102 soil moisture monitoring sites. The validated soil moisture is used in combination with in situ groundwater data to quantify total water storage change (TWSC) in the region. The estimated storage change is in turn compared with gravity recovery and climate experiment‐derived TWSC for the study area. The soil moisture and TWSC terms show favourable agreements, with discrepancies of < 10% on the average. While there is no consistent seasonal trend in soil moisture, TWSC shows a strong seasonality. It is low in spring and high in summer. This trend corresponds with the IRR–PPT season in the study area. Change in groundwater and total water storage indicates storage depletion in the basin. Storage depletion in the region is driven mainly by groundwater IRR and ET loss. Despite the low PPT and high ET, there is narrowing seasonal trend in soil moisture. This is achieved at the expense of groundwater storage. IRR pumping has induced extensive groundwater depletion in the basin. It is therefore vital to develop cultivation strategies that aim at limiting IRR pumping and ET loss. Water management practices that not only reduce waste but also ensure high productivity and ecological sustainability could also mitigate storage depletion in the region. These measures could reduce further not only the seasonal trend in soil moisture but also that in groundwater storage. Copyright © 2011 John Wiley & Sons, Ltd.     

Artificial neural network models for estimating regional reference evapotranspiration based on climate factors

Evapotranspiration (ET) is one of the basic components of the hydrologic cycle and is essential for estimating irrigation water requirements. In this study, an artificial neural network (ANN) model for reference evapotranspiration (ET₀) calculation was investigated. ANNs were trained and tested for arid (west), semi‐arid (middle) and sub‐humid (east) areas of the Inner Mongolia district of China. Three or four climate factors, i.e. air temperature (T), relative humidity (RH), wind speed (U) and duration of sunshine (N) from 135 meteorological stations distributed throughout the study area, were used as the inputs of the ANNs. A comparison was conducted between the estimates provided by the ANNs and by multilinear regression (MLR). The results showed that ANNs using the climatic data successfully estimated ET₀ and the ANNs simulated ET₀ better than the MLRs. The ANNs with four inputs were more accurate than those with three inputs. The errors of the ANNs with four inputs were lower (with RMSE of 0·130 mm d^?1, RE of 2·7% and R² of 0·986) in the semi‐arid area than in the other two areas, but the errors of the ANNs with three inputs were lower in the sub‐humid area (with RMSE of 0·21 mm d^?1, RE of 5·2% and R² of 0·961. For the different seasons, the results indicated that the highest errors occurred in September and the lowest in April for the ANNs with four inputs. Similarly, the errors were higher in September for the ANNs with three inputs. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrological processes of a rainforest headwater swamp from natural chemical tracing in Nsimi watershed,Cameroon

The hydrological role of a headwater swamp in a tropical rainforest is studied using chloride mass balance (CMB) and end‐member mixing analysis. There are three main contributions to streamflow: (1) the hillside bedrock aquifer, (2) overland flow from the swamp during storm events and (3) groundwater flow from the swamp aquifer. Before rainfall events of the wet season, the pre‐event water comprises a mix of 80% of bedrock aquifer and 20% of swamp aquifer. During storms, the relative contribution of overland flow increases according to the rainfall intensity and the initial saturation rate of the pre‐event water reservoirs. The yearly contribution of overland flow from the swamp to the stream is about 31%. The relationship between the swamp and the stream fluctuates with space and time. Generally, the swamp is drained by the stream; however, at the end of long dry seasons, after the first rains, indirect recharge occurs from the stream to the swamp with a hydraulic gradient inversion in the swamp aquifer. The net contribution of the swamp aquifer to the stream is only 4%, which is much lower than the hillside aquifer contribution of about 65%. Recharge on the swamp being very low, these results suggest that, except for a few storms at the end of the dry season, the Nsimi swamp does not contribute to flood attenuation. Evapotranspiration is higher on the hillside than in the swamp. Nevertheless, depletion of water stored within the swamp is dominated by evaporation rather than by its contribution to streamflow. The export of solutes through swamp groundwater flow below the weir is low (<7%). Nevertheless, the swamp is the most active area of weathering in the watershed. Copyright © 2011 John Wiley & Sons, Ltd.     

A soil‐water‐balance approach to quantify groundwater recharge from irrigated cropland in the North China Plain

Rapidly depleting unconfined aquifers are the primary source of water for irrigation on the North China Plain. Yet, despite its critical importance, groundwater recharge to the Plain remains an enigma. We introduce a one‐dimensional soil‐water‐balance model to estimate precipitation‐ and irrigation‐generated areal recharge from commonly available crop and soil characteristics and climate data. To limit input data needs and to simplify calculations, the model assumes that water flows vertically downward under a unit gradient; infiltration and evapotranspiration are separate, sequential processes; evapotranspiration is allocated to evaporation and transpiration as a function of leaf‐area index and is limited by soil‐moisture content; and evaporation and transpiration are distributed through the soil profile as exponential functions of soil and root depth, respectively. For calibration, model‐calculated water contents of 11 soil‐depth intervals from 0 to 200 cm were compared with measured water contents of loam soil at four sites in Luancheng County, Hebei Province, over 3 years (1998–2001). Each 50‐m² site was identically cropped with winter wheat and summer maize, but received a different irrigation treatment. Average root mean‐squared error between measured and model‐calculated water content of the top 180 cm was 4·2 cm, or 9·3% of average total water content. In addition, model‐calculated evapotranspiration compared well with that measured by a large‐scale lysimeter. To test the model, 12 additional sites were simulated successfully. Model results demonstrate that drainage from the soil profile is not a constant fraction of precipitation and irrigation inputs, but rather the fraction increases as the inputs increase. Because this drainage recharges the underlying aquifer, improving irrigation efficiency by reducing seepage will not reverse water‐table declines. Copyright © 2003 John Wiley & Sons, Ltd.     

Reedbed evapotranspiration rates in England

Measurements of evapotranspiration from contrasting stands of Phragmites australis [ET(Reed)] were obtained over several years at three sites within England between 1994 and 1998. A comparison with published ET(Reed) values showed the UK rates to be considerably lower than those measured in continental Europe. From the ET(Reed) data monthly crop coefficients [K_c(Reed)] have been developed, which when used with Reference Crop Evapotranspiration will enable reedbed water use to be determined. Due to the differences in study site characteristics, values for K_c varied widely, and it was not considered appropriate to combine results to produce a single set of monthly mean values. However, suggestions are made regarding the application of the K_c(Reed) values to wetland design. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of Temporal Resolution of NDVI on Potential Evapotranspiration Estimation and Hydrological Model Performance

Normalized difference vegetation index (NDVI) data, obtained from remote sensing information, are essential in the Shuttleworth-Wallace (S-W) model for estimation of evapotranspiration. In order to study the effect of temporal resolution of NDVI on potential evapotranspiration (PET) estimation and hydrological model performance, monthly and 10-day NDVI data set were used to estimate potential evapotranspiration from January 1985 to December 1987 in Huangnizhuang catchment, Anhui Province, China. The differences of the two calculation results were analyzed and used to drive the block-wise use of the TOPMODEL with the Muskingum-Cunge routing (BTOPMC) model to test the effect on model performance. The results show that both annual and monthly PETs estimated by 10-day NDVI are lower than those estimated by monthly NDVI. Annual PET from the vegetation root zone (PETr) lowers 9.77%-13.64% and monthly PETr lowers 3.28%-17.44% in the whole basin. PET from the vegetation interception (PETi) shows the same trend as PETr. In addition, temporal resolution of NDVI has more effect on PETr in summer and on PETi in winter. The correlation between PETr as estimated by 10-day NDVI and pan measurement (R2= 0.835) is better than that between monthly NDVI and pan measurement (R2 = 0.775). The two potential evapotranspiration estimates were used to drive the BTOPMC model and calibrate parameters, and model performance was found to be similar. In summary, the effect of temporal resolution of NDVI on potential evapotranspiration estimation is significant, but trivial on hydrological model performance.     

Effects of Climatic Change on Evapotranspiration in Zhalong Wetland, Northeast China

1 Introduction As a result of persistent increase in carbon dioxide in the atmosphere since the 1950s, global and regional climate features, such as temperature and precipitation, have ob- viously changed (Yu et al., 2002). The General Circulation Models (GCMs) provide potential climate scenarios by studying the effects of carbon dioxide on the temperature. Tickell (1993) predicted that the mean temperature will increase by 1℃ till the year 2050 and by 3℃ at the end of the 22th century. S…     

余量称重法在土壤蒸散测量中的应用

土壤水分的蒸散能力与蒸散量的大小是研究干旱灾害的一个重要参数。由于没有长时间大范围的观测数据资料,目前水文气象研究干旱结果仍然局限在单点或者小范围的实验研究及数值模式中,没有时空变化的代表性。余量称重法的方式,可以较为直观地得到土壤中水分蒸散的量及其量值变化规律,对土壤蒸散能力有一个量化的概念。此方法操作简便,代表性强,对干旱研究将起到一定的作用。与数模测量法相比较,余量称重法的测量数据无需考虑气象环境中辐射与空气气温、湿度、风速大小和降水四个方面因素的影响,可以直接运用到气象、水文、水利及相关需要的测量与研究行业当中。