Estimating groundwater required for the sustainability of Prosopis cineraria (L.) druce and ziziphus spina-christi (L.) Desf. forests in Faryab county, Kerman province, Iran

Prosopis cineraria (L.) druce and Ziziphus spina-christi (L.) Desf. are important species of Sahara-Sindhi vegetation. While being native, they have good adaptability, growth and regeneration. This study was conducted to estimate the amount of groundwater required for the sustainability of Z. spina-christi and P. cineraria natural forests in the watershed of Faryab county in Kerman province, Iran. First, using Google Earth images, networking establishment of ninety plots of 100 m2 in one-hectare networks, the average number of Z. spina-christi and P. cineraria trees were counted. Then, using the minimum water requirement of trees, estimated based on lysimetric studies, water consumption of Z. spina-christi and P. cineraria trees in the area was calculated. Using the MODFLOW model, the groundwater balance situation in Faryab plain aquifer for 2017-2018 was calculated. Having the volume of water consumption of Z. spina-christi and P. cineraria in the region, water balance and aquifer storage coefficient, the impact of the forests on groundwater of Faryab plain was calculated. The results showed that the average number of P. cineraria trees is 250 individuals and Z. spina-christi tree stands are 30 individuals per hectare. The results of the study of water balance and groundwater aquifer show a volume deficit of 25 million cubic meters of the reservoir and a 26-meter drop in groundwater level over the past two decades. According to the water balance calculated, the uncontrolled extraction of water by agricultural wells, which is about 160 million cubic meters per year, has caused such a decline in the region. Considering the importance of Z. spina-christi and P. cineraria trees for this ecosystem as the main species, the water right of this forest was estimated to be 2.6 million cubic meters per year in the planning of water resources in the Faryab plain.