Response of Water Cycle Processes in Sanjiang Plain to Human Activities and Climate Change in Recent 50 Years

Abstract

Impacts of human activities on water cycle process in Sanjiang plain mainly include:①large-scale hydro-junction project dramatically weakened the flood processes of Heilongjiang,Wusuli and Songhua Rivers flowing through Sanjiang plain sections,and reduced natural groundwater and surface water recharges opportunities and amount for Sanjiang plain;②construction of large number of drainage canals enhanced the hydrological gradient of regional drainage,and accelerated the generation and distribution processes of surface runoff;③conversion from glebe into paddy field enhanced the utilization efficiency of effective precipitation,reduced the regional surface runoff depth,and enlarged the regional evapotranspiration;④area enlargement of well-irrigated rice field drives large-scale groundwater exploitation,which leads to the imbalance of exploitation and recharge of groundwater,the continuous decline of the groundwater table,and the reduction of groundwater storage volume;⑤deforestation in the headstream region,which causes the reduction of the proportion of snowfall converting into surface runoff and the decline of water conservation capabilities of forest soil.The resulting influences human activities have on water cycle processes in Sanjiang plain are that water input is decreasing and water output is increasing.Major impacts from climate change on water cycle process mainly include:①total area precipitation shows a declining trend,but not obvious;②regional temperature and potential evaporation are rising;③the rise of land temperature is the most obvious,the permafrost layer is becoming thinner,duration of permafrost fusion is shortened by 55 to 62 days,and the soil moisture of permafrost layer is apparently lower than that 50 years ago.Cultivated soil water moisture visibly declines.These changes will not benefit the surface runoff generation and precipitation infiltration to recharge groundwater,Based on the water cycle processes analysis,it is concluded that Sanjiang plain is getting drought.Therefore,strengthening the development and application of agricultural conservation tillage measures,as well as speeding up the restoration of degraded wetland water resources,enhancing the regional water storage capacity and water saving level in agricultural aspect will be important directions to ensure Sanjiang plain water security.