Study On Spatial And Temporal Variation Of Water Deficit In Heihe River Basin From1960to2009

Water is the most active ecological factor and precious natural resource in thesemi-arid and arid region. Water shortage became the main contradiction betweenecological agriculture and sustainable development. Water deficit reflect the quality of thewater condition from two aspects of moisture－income and expenditure, vividly reflect theinfluence degree of climate condition on water profit and loss of crops, is significantindicator of regional agricultural drought in the climate, and has the representative ofbiological and climatology meaning. Heihe river basin locates in arid region of northwest.Along with urbanization accelerates and industry and agriculture rapid development inrecent years, various departments’water consumption grows suddenly, and a series ofecological problems has occurred in Heihe river basin and has always been great concernby the state and government. So studying the change characteristics of water deficit inHeihe river basin help us to in-depth understand the effect of the climate change onhydrology and water resource, and it has a very important meaning to social-economicdevelopment, ecological environment protection and water resource management of Heiheriver basin.The analysis of water deficit was based on the meteorological datasets from1960to2009in16stations of the Heihe river basin. Potential evapotranspiration was computed byusing FAO Penman-Monteith model with these meteorological datasets. Water deficit wasdefined as a gap of precipitation to potential evapotranspiration. The temporal and spatialvariations of water deficit in the Heihe river basin were carefully analyzed in this study.This article draws following conclusions:(1)The annual-average water deficit in the Heihe river basin ranged from-1387mm to-269mm with the spatial variation pattern of increasing gradually from east to west, fromnorth to south and from northeast to southwest. In terms of season, magnitudes of waterdeficit mainly concentrated in summer and spring, accounting for37%and35%of thetotal for a year, respectively, followed by autumn and winter.(2)Water shortage was a common phenomenon, and the annual water deficit generallyexhibited an increasing trend in the Heihe river basin in recent50years. The largest andlowest value of water shortage occurred in the1970s and1990s, showing816mm and746mm, respectively. Water deficit showed an increasing trend, and the clmate had a tendency towards drought during recent10years. Water deficit decreased weakly in winter,however, increased in other seasons, but only the increasing trend of summer could evenpass the significance test at the level of P<0.05. The persistence of change trends of waterdeficit with the time was very strong in summer, followed by the mean annual and spring,and was relatively weak in autumn and winter. Magnitudes of water shortage mainlyconcentrated in later spring and early summer, and it would bring a comparative influenceupon agricultural production. Yearly water deficits of the upper, middle and lower reachesof the basin fluctuated obviously with the coefficient of variation for each were-16.12%,-6.97%,-5.80%.(3)The spring and winter water deficits in most parts of Heihe river basin decreased,which showed a generally drying trend, and the summer, autumn and mean annual waterdeficits increased, which showed a generally wetting trend. Wetting trend had beenparticularly apparent in the summer season.(4)Yearly water deficit had period characteristic, water deficit of the whole region,upper, middle and lower reaches generally showed the main cycle of19,8,19and25years,respectively. Moreover, water deficit also had abrupt property as other meteorologicalfactors, water deficit of the whole region and the middle reaches showed an abrupt increasein1978, the upper reaches showed no abrupt property, while the lower reaches showed anabrupt decrease in1969and an abrupt increase in1978.(5)The leading factor affecting water deficit of the Heihe river basin was precipitation,and the changes of other climate elements can enhance or weaken the changes of the waterdeficit. When spring comes, the wind speed becomes the key factor influencing waterdeficit. It was found that temperature significantly affected water deficit in winter.