Abstract
The Zayanderud Basin is an important agricultural area in central Iran. In the Basin, irrigation consumes more than 90 percent of the water used, which threatens both the downstream historical city of Isfahan and the Gavkhuni Wetland reserve—the final recipient of the river water. To analyze impacts of land use changes and the occurrence of metrological and hydrological drought, we used groundwater data from 30 wells, the standardized precipitation index (SPI) and the streamflow drought index (SDI). Changes in the wetland were analyzed using normalized difference water index (NDWI) values and water mass depletion in the Basin was also assessed with gravity recovery and climate experiment (GRACE)-derived data. The results show that in 45 out of studied 50 years, the climate can be considered as normal in respect to mean precipitation amount, but hydrological droughts exist in more than half of the recorded years. The hydrological drought occurrence increased after the 1970s when large irrigation schemes were introduced. In recent decades, the flow rate reached zero in the downstream part of the Zayanderud River. NDWI values confirmed the severe drying of the Gavkhuni Wetland on several occasions, when compared to in situ data. The water mass depletion rate in the Basin is estimated to be 30 (±5) mm annually; groundwater exploitation has reached an average of 365 Mm3 annually, with a constant annual drop of 1 to 2.5 meters in the groundwater level annually. The results demonstrate the connection between groundwater and surface water resources management and highlight that groundwater depletion and the repeated occurrence of the Zayanderud River hydrological drought are directly related to human activities. The results can be used to assess sustainability of water management in the Basin.
Highlights
Arid and semi-arid climatic regions are important agricultural zones, as they host 41.3 percent of the world’s population [1]
Due to irrigation and reduced river flow, hydrological drought was recorded in 60% of the year in the Zayanderud River flow, streamflow drought index (SDI) value less than 0
The constant reoccurrence of the hydrological droughts is directly related to the human activities in the Basin
Summary
Arid and semi-arid climatic regions are important agricultural zones, as they host 41.3 percent of the world’s population [1]. 14.7 percent of the farmed areas are irrigated in arid and semi-arid climatic zones, an important contributor in crop production [2]. As fully irrigated areas have two to three times higher crop yields than the rainfed areas, fully irrigated areas are increasing in dry regions [3]. The introduction of irrigation has increased agricultural drought occurrence since the mid-20th century [4] and stream flow depletion has led to wetlands loss [5]. The annual global groundwater depletion is estimated to be 283 (±40) km3 [6].
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