Variation characteristics of non-rainfall water and its contribution to crop water requirements in China’s summer monsoon transition zone

Abstract

Comprising mainly fog water, dew water, and water-vapor adsorption (WVA), non-rainfall water (NRW) makes an important contribution to the local ecology in the arid and semi-arid regions. Although NRW components have been studied individually in previous work, little attention has been paid to the integrated characteristics of NRW and the corresponding relationships among the components. In fact, few other studies have considered how NRW components form and change, let alone how they contribute to land surface water (LSW) balance and influence crop water requirements in China. In this paper, a method will be established for identifying components of NRW, based on a combination of lysimeter measurements and micro-meteorological data from Dingxi Station in the summer monsoon transition zone (SMTZ) of China. Diurnal time series of NRW components will be given. The relationship between NRW and climatic and environmental factors is then analyzed. Finally, the diurnal and annual variations of NRW and how they contribute to LSW balance and crop water requirements are discussed. The results show that the influence of climatic and environmental conditions to occur dew and WVA is different even opposite affects such as relative humidity to that. There is negative feedback between soil moisture and WVA; this does not hold, however, for dew. The variation characteristics of dew and WVA are different. Their diurnal variation shows the complementary characteristics of each other. Not only that, the annual distribution of NRW also complemented with that of precipitation. Although NRW contributes to no more than 15% of the water balance in a full year, NRW plays a leading role during the non-monsoon period, wherein the amount of NRW is 1–3.5 times that of precipitation. Moreover, it is just the period of soil water conservation and sowing date for crops such as winter wheat. Therefore, the existence of NRW is fundamental for alleviating agricultural drought. It explained that NRW has great significance for reducing agricultural losses and understanding the LSW balance in the SMTZ.