Modeling Effects of Rainwater Harvesting Systems on Water Yield Increase and Non-beneficial Evaporation Reduction to Sustain Agriculture in a Water-scarce Region of China

摘要

The northwestern region of China, which has an arid/semiarid climate, relies heavily on agriculture to provide food for the growing population. Climate change is affecting water availability in the region, causing long periods of drought and water scarcity followed by shorter periods of heavy rainfall and excess water availability. The ridge and furrow rainwater harvesting systems (RFRWHS) are a means of solving the problem of water scarcity; the systems can replenish soil moisture, reduce non-beneficial evaporation from bare soils, and increase surface water yield. In such a region, the hydrologic cycle is dominated by soil evaporation, leading to minimal surface runoff and depletion of soil water. For this thesis, hydrologic models were developed to predict the effects of the RFRWH systems on increases in water yield and reduction of non-beneficial evaporation. The results indicate that water yield will increase with increasing ridge width, and the systems with a common plastic mulch or biodegradable plastic mulch are most effective in increasing water yield. These two mulches may be good choices for increasing water availability and adapting to climate change. Potential evapotranspiration (PET) models are a tool used to measure non-beneficial evaporation. PET models results showed that PET tended to increase over the past several years, possibly due to climate change, while the average soil evaporation during the growing seasons (April to October) was reduced by 40% due to the RFRWH systems. This reduced soil evaporation may have increased the water available for crops in the furrows, thus increasing crop yields. The percentage of precipitation lost to non-beneficial soil evaporation may have been reduced as much as 30% by using the RFRWH systems.