Long-Term Climate Impacts on the Hydrological Cycle of Northeastern Puerto Rico due to the Combined Effects of LCLU and Global Climate Changes

The overall goal of this project is to gain a better understanding of the climate changes due to the combined effects of land cover and land use (LCLU) changes, anthropogenic activity, and increasing global temperatures (GW) in tropical coastal areas, regions where global, regional and local climate phenomena converge. To achieve the high-level research goal of understanding these combined climate effects (LCLU + GW), the heavy populated Caribbean island of Puerto Rico was taken as the testing case. The research uses an integrated approach of high-resolution remote sensing and climatological data, linked to the Regional Atmospheric Modeling System (RAMS), which was employed to perform ensembles of climate simulations (combining 2-LCLU and 2-global climate scenarios). Reconstructed agricultural maps (1951-1956) are used to define past LCLU, and combined with reconstructed sea surface temperatures (SST) for the same period form the Past climate scenario, while the Present (2000-2004) scenario was supported with the high resolution remote sensing data (10-m-res). The climate reconstruction approach is validated with observational data from both the past and present timeframes. The selection of the two climate scenarios considers large-scale bias (i.e. ENSO/NAO) as reflected in the region of interest. Direct and cross comparison of the results allows the quantification of single, combined, and interactive effects. Results indicate that increased surface winds and more easterly trade winds in the Present timeframe disrupts a climatological pattern of inland moisture advection and convergence in the mountain range ridge, affecting cloud formation and rain development in the region. In terms of the initial stages of the hydrological cycle, the GW signal proves to have an overwhelming effect on increasing cloud base heights over high elevations, along with a reduction of total column liquid water content, represented by both cloud droplets and raindrops. The combination of higher clouds and less water content in the atmospheric column produce a dramatic reduction in surface accumulated precipitation over the Central Mountains of Puerto Rico and El Yunque, a tropical montane cloud forest located east of San Juan and managed by the US Forest Service. Results of the research may have relevance in other tropical coastal locations exposed to significant changes in land use.