Quantifying the relationship between evaporation and precipitation variations and mangrove health: Insights from a Mangrove Islands in Belize

Along tropical coastal intertidal zones, mangroves provide numerous beneficial ecosystem services such as coastal defense, blue carbon storage, and fauna and flora habitat. Despite their socioeconomic and biological importance, mangroves are under threat due to a number of factors, including deforestation, pollution, and droughts. In particular, droughts result from a deficit in precipitation with respect to evaporation rates over prolonged time periods, which can lead to an increase in the concentration of soil stressors such as sulfide as sulfate and consequently a decrease in mangrove health. To quantify the relative importance of changes in evaporation and precipitation rates on mangrove response with respect to other factors, we analyze a low-lying mangrove island in Belize, where human development, freshwater inputs from land, and overland flow are negligible. First, we determined a normalized difference vegetation index based on Landsat 8 satellite data as a proxy for mangrove health from 2013-2022 and found that mangrove health generally improves during the wet season (June through November) and declines during the dry season (December through May). Second, we extracted precipitation and evaporation rates from publicly available satellite data and found that net evaporation rates (i.e., evaporation minus precipitation rates) are generally negatively correlated with our metric for mangrove health. That is, when the net evaporation rate increases increase, the percentage of mangrove area under stress increases and vice versa. Consistent with previous work, these results suggest that net evaporation rates are a good predictor of mangrove stress and potentially mangrove area loss.