On the Changes of the Hydrological Balance of Caribbean Lakes – Modeling and Observations

The Enriquillo and Sumatra are saltwater lakes located in a rift valley that is a former marine strait created around 1 million years ago when the water level fell and the strait was filled in by river sediments, they are the largest lakes in the Dominican Republic and Haiti, respectively, with Lake Enriquillo being the lowest point in the Caribbean. The lakes, part of the Enriquillo closed water basin in the southwestern region of the island of La Hispaniola, have been experiencing dramatic changes in total lake-surface area coverage during the period 1980-2012. The size of the lakes was determined using remote sensing images (NASA-LANDSAT) analyzed with geographic information system (GIS) at different times during the available record. The size calculation for Lake Enriquillo shows a lake surface area of approximately 276 km2 in 1984 that gradually decreased to 172 km2 in 1996. After a period of fluctuations between 1996 and 2001, the surface area of the lake reaches its lowest point in 2004, at 165 km2. Beginning in 2004, the recent growth of the lake begins and reaches its 1984 size in 2006. Based on surface area measurement for December 2009, the lake size is 333 km2, 17% larger than in 1984 and almost double than in 2004. Sumatra sizes at both ends of the record are 115.96 km2 in 1984 and 134.26 km2 in 2011, an overall 15.8% increase in 27 years. Because the lakes are mostly latitudinally restricted by topography, most of the size changes occur on the southeastern side of Lake Enriquillo, with some growth on the western tip. Determining the causes of lake surface area changes is of extreme importance due to the environmental, social and economic consequences. In 2009 more than 18,865 hectares of agricultural land around the lake were flooded impacting 16 communities and some 10,000 families. The international highway dividing the two countries is submerged, impacting the commercial traffic and associated economic activity. The goal of this study is to quantify the changing water balance in these lakes using satellite and ground observations and regional atmospheric modeling. Analyses of environmental variables in the region reflect a hydrological unbalance of the lakes due to changing regional hydro-climatic conditions. Historical data show precipitation, land surface temperature and humidity, and sea surface temperature (SST), increasing all over the past decades. Salinity levels have also been decreasing by more than 30% from baseline levels. We hypothesized that the increases in SSTs may be leading to increases in regional moisture content which leads to decreases in evaporation capacity from the lakes, and simultaneously to increases in fresh water production in the neighboring sierras. A network of rain and fog gauges along the high sierras reflects growing cloud mountane forests, with significant increase in water production. Results from a high resolution atmospheric modeling (RAMS at 1km) clearly reflect increases in the amount of precipitable water content in the vertical column as function of changing regional climate conditions.