Modeling net water requirements for wetlands in semi-arid regions

Abstract

Wetlands in arid and semi-arid regions often experience water shortage problems due to interrupted water supply. Rapid population growth and economic development have caused deterioration or total destruction of many wetlands in such regions. Protection or restoration of these wetlands require a good understanding of the relationship between water supply and the soil wetness. This paper presents a model simulation study of such a relationship based on weather and soil data from Xi’an, China. The study area has an average annual precipitation of 600 mm and evaporation of 1200 mm. The simulation results showed that, to produce a certain wet condition, the required amount of water supply varied with recharging time due to different evapotranspiration rates. To maintain a consecutive water table depth within 30 cm (1) for 5% of the growing season, water requirements varied from 7 cm to 16 cm for different recharging months; (2) for 12.5% of the growing season, water requirement varied from 9 cm to 20 cm; and (3) for 25% of the growing season, water requirements varied from 13 cm to 27 cm. The highest water requirement occurred in summer when the air temperature is the highest of the year. Simulation results also showed that the timing of recharge not only has an important effect on the threshold water requirement, but also on the overall soil wetness of a year. Recharging at earlier time of the growing season produced longer wet periods, but the overall water table remained low during the rest of the growing season. Later inflow only influenced the water table for a small portion of the growing season, but it maintained a generally high water table in winter months and the early part of the next growing season.