No abstract

Snowmelt contributions to water resources in cold regions are receiving increasing attention. However, there are clear challenges to accurately distinguish the snowmelt contributions to different hydrological processes in seasonal snow regions. Here, we present an improved method to evaluate snowmelt contributions by tracing the snowmelt flow paths in different media based on a distributed geomorphology‐based ecohydrological model coupled with a physically based snow module. The calculated snowmelt contribution is not limited to river discharge but is also applicable to evaporation and soil storage. The study region, the upstream Heihe River (UHR) basin, is located in the northeastern Tibetan Plateau. Our results indicate that snowmelt can continuously contribute to hydrological processes throughout the year because most of the snowmelt remains in soil voids, even on snow‐free days. In UHR, the snowmelt contribution to total runoff on snow days accounts for a minor part of the total snowmelt contribution, and the snowmelt contribution on snow‐free days accounts for a major part of the total. There is notable snowmelt retention in the soil in each year, which continues to supply discharge into next year. Our results also indicate that the role of snowmelt contribution to annual discharge could be gradually weakened if rainfall more greatly increases the summer discharge in the UHR basin. The improved evaluation method will contribute to a more comprehensive assessment of snowmelt contributions to hydrological processes in seasonal snow regions.

Abstract. The spatial and temporal variations of snowcover distribution, and snowmelt runoff are considered as sensitive indicators for climatic change. The purpose of this paper is to analyze and forecast the responses of snowmelt runoff to climate change in an inland river basin. The upper basin of Heihe River in Northwestern China was chose as the study area, and the observation data from the meteorological and hydrological stations were utilized to analyze the status and regularity of the climatic change over the past 50 years. Snow cover area was obtained by an optimized technology using Moderate Resolution Imaging Spectroradiometer data with Normalized Difference Snow Index adjustment and topographic correction. A concept of potential snowmelt was suggested to illustrate the response of spatial snowmelt to climate change. The results show that the annual SCA proportion and the potential snowmelt keep an increasing trend since 2000. There is a negative relationship between annual air temperature and SCA proportion from 2000 to 2008. Snowmelt Runoff Model was chose to simulate snowmelt runoff and scenario forecast the change trend of snowmelt runoff in this region. The results show that climatic warming was apparent in the upper basin of Heihe River over the past 50 a. Annual average air temperature of three different weather stations located in the basin has increased 2.1 • C, 2.6 • C and 2.9 • C respectively from 1956 to present. The snowmelt runoff has increased obviously from 1970 to present. With different warming climate scenarios, the results by using SRM simulating showed that the first occurred time of snowmelt runoff shift ahead and discharge become larger as responses of snowmelt runoff to air temperature increasing, and the influence of temperature rising on average discharge of the whole snow season is not obvious.

Abstract:Sustainable water use is in serious crisis in the piedmont region of the Taihang Mountains in the North China Plain, owing to rapid groundwater drawdown. Estimating the water requirement for agriculture, the biggest user of groundwater, will be helpful in understanding groundwater decline. Through the use of DSSAT-3Ð5 wheat and maize models, we assessed water use in winter wheat and maize, two staple crops in the region, in [1987][1988][1989][1990][1991][1992][1993][1994][1995][1996][1997][1998][1999][2000][2001]. Trends between groundwater change and simulated agricultural water use were compared. The results showed that groundwater decline was sensitive to simulated crop water requirement and irrigation requirement. According to regression analysis, 100 mm of water requirement by cultivated land (mainly wheat and maize) resulted in about 0Ð64 m of groundwater decline. This relationship might be useful in understanding the regional water balance and to help decision-makers control groundwater decline through controlling crop water use or through long-distance water transfer. The study demonstrated the usefulness of using the DSSAT model for estimating crop water use and the effectiveness of clarifying the reason for groundwater decline using the simulation results of water use.