USING GRACE DATA TO MONITOR EFFECTS OF ANTHROPOGENIC MODIFICATION AND CLIMATE CHANGE ON GROUNDWATER IN THE ARAL SEA REGION: 2002-2012

The Aral Sea watershed located in central Asia has seen significant anthropogenic modification since the mid 20^th century, leading to a decrease in size of the sea by almost 90%. The watershed is a closed basin with an area of almost 2 million square kilometers which includes both the Amu Darya and Syr Darya river systems. A network of canals and channels has diverted a significant amount of flow from both rivers into various agricultural areas and reservoirs. Groundwater is an extremely important resource in the region providing the majority of river flow during winter months, while glacial melt provides up to 70% during the summer months in hot years.

GRACE (Gravity and Climate Experiment) data from 2002-2012 was used to monitor total water storage trends within the basin using a linear model. The data was normalized with an annual periodic function to remove seasonality. The GLDAS (Global Land Data Assimilation Systems) model was used to estimate the monthly mass of soil moisture and snow cover. Total surface water mass was estimated using satellite imagery and historical topographic maps.

Much of the water diverted from the Syr Darya and Amu Darya remains stored as groundwater recharge and growing artificial lakes which supports the regions agriculture. However, the water balance of the whole watershed shows an overall negative trend in water storage due to evaporative losses from these diversions. A positive trend in groundwater storage mass was observed in agricultural areas and in the vicinity of the reservoirs in the central part of the basin.

Opposite trends were observed in the headwaters of both glacial-fed rivers within the Aral Sea basin. Total summer time snow cover area was determined for both rivers using Landsat imagery. An increase in total snow/ice cover in the Amu Darya headwaters was observed and a decrease in total snow/ice in the Syr Darya. The Amu Darya receives precipitation from the South Asian Monsoon which has increased in the last decade. The more northern headwaters of the Syr Darya River receive continental precipitation of which previous studies have shown no significant trends, but an increase of 1-2 degrees C over the past century may explain loss in mass due to glacial ablation. Future water and food security in the region depends on accurate monitoring and predictions of water resources in the future.