Rain Variability and Population Growth to Explain Historical Levels of the Patzcuaro Lake in Mexico

Abstract

The height variability of Lake Patzcuaro, in central Mexico, remained constant for several decades, and during that period, the lake maintained its functionality and environmental services. However, in the last twenty years, there has been a significant decrease in the variability range. In order to estimate the water balance, in this work, an approach was developed to understand how water moves in time and space, and to determine possible inherent thresholds to lake variability. The historical Lake Patzcuaro height above 2035 masl was correlated with several climatic variables. The correlation with monthly rainfall shows that there is a delay of three months, indicating that the lake volume depends on three factors: precipitation, surface runoff and underground contribution, of which precipitation over the lake surface is the least significant. In the long term, using annual data, there is a remarkable memory of precipitation extending beyond five years, seen as a correlation with the accumulated precipitation anomaly ( r 2 = 0.76). This behavior should be explained by understanding relationship between the lake and its aquifer. Also important is the population growth, which affects the lake level in two ways: water extraction and water discharge. The models pointed out a nonlinear relationship between water level and the aforementioned variables, and suggest that the carrying capacity of the basin is around 90 thousand people, under current patterns of water consumption. It also indicates that, in order to allow lake recovery or to maintain system resilience, the anomaly of precipitation accumulated during several years should exceed 1000 mm. Although a correlation with land use was attempted, historical data do not reflect a trend that could be associated with water balance.