Satellite observation of atmospheric CO₂ and water storage change over Iran

Like many other Middle East countries, Iran has been suffering from severe water shortages over the last two decades, as evidenced by significant decline in surface water and groundwater levels. The observed changes in water storage can be attributed to the mutually reinforcing effects of human activities, climatic variability, and of course the climate change. The objective of this study is to analyze the dependency of atmospheric CO₂ increase on the water shortage of Iran, for which we investigate the spatial relationship between water storage change and CO₂ concentration using large scale satellite data. We conduct our analysis using water storage change data from GRACE satellite and atmospheric CO₂ concentration from GOSAT and SCIAMACHY satellites during 2002-2015. To analyze the long-term behavior of time series we benefit from Mann-Kendal test and for the investigation of the relationship between atmospheric CO₂ concentration and total water storage we use Canonical Correlation Analysis (CCA) and Regression model. Our Results show that the water storage change anomaly and CO₂ concentration are negatively correlated especially in northern, western, southwest (Khuzestan province), and also southeast (Kerman, Hormozgan, Sistan, and Baluchestan provinces) of Iran. CCA results reveal that in the most of northern regions, the decrease in water storage is significantly influenced by the increase of CO₂ concentration. The results further show that precipitation in the highland and peaks does not seem to be influenced by the long and short-term variation in CO₂ concentration. Besides, our results show that the CO₂ concentration is slightly correlated with a weak positive trend in evapotranspiration over agricultural areas. Thus, the indirect effect of CO₂ on increasing evapotranspiration is observed spatially in the whole of Iran. The results of the regression model between total water storage change and carbon dioxide (R² = 0.91)/water discharge/water consumption show that carbon dioxide has the highest effect on total water storage change at large scale. The results of this study will contribute to both water resource management and mitigation plans to achieve the goal of CO₂ emission reduction.