Water balance in red soil hilly regions of Southern China under drought climate situations

Abstract: The water and land resources matching situation is not optimistic, by that the arid climate events occur frequently in Southern China under the background of global warming in recent years. Taking Jitai Basin as an example, we systematically diagnosed drought situation of the past 50 years and identified the type and intensity of the drought by using standardized precipitation index. Moreover, we built a water balance model to analyze the water balance on cultivated land, forest land in red soil hilly regions of Southern China under the drought climate conditions. The results showed that drought events occurred with a higher frequency in nearly 30% during 1960 to 2010 in Jitai Basin, in which the light drought occurred frequency was the most, followed by the special drought, the middle drought and heavy drought. Drought events occurred mostly in autumn, and the spring and winter drought have occurred occasionally. The water balance of early rice, rape, forest land and shrub land in the water surplus in Jitai Basin mainly characterized by moisture surplus, and the rice water deficit rate was at 30% level under no-arid climatic conditions. The volume of water balance in Jitai Basin was about 448mm under no-arid climatic conditions, which indicated that the natural precipitation could meet the water demands of the major land type on the whole, including forest and cultivated land etc. Water surplus was the basic characteristic, and the distribution of water surplus in valley and plain was lower than in hilly and mountain. Under the different drought climate conditions, the water balance volume of cultivated land was -87, -104, -356 and -553mm, and the water balance of cultivated land in Jitai Basin turned to deficit, with the drought degree aggravating, the water deficit of cultivated land was significantly enhanced, the effects of drought on the water balance of cultivated land were obvious. From the changes of the spatial pattern, the deficit situation of cultivated land was gradually expanded from the central basin valley plains to the hilly areas. The water balance volume of forest land was 376、271、200 and144mm, while the water surplus of forest land fell in the range of 37.87%-77.80%, With the drought degree aggravating, the water surplus of forest land was overall decreased. From the spatial variations, the water surplus of forest land was decreased from valley plain area to hilly and mountain area. When the light, middle and heavy drought happened, the volume of water balance in Jitai Basin was 215、142 and19 mm, declined respectively by 55.07%, 70.28% and 96.08%. When the special drought events occurred, water shortage amounted to 72 mm. In a word, water surplus was deceased and water deficit was increased in Jitai Basin as its drought degree intensifying.