Aridity Indices to Assess Desertification Susceptibility: A Methodological Approach Using Gridded Climate Data

Desertification is a land degradation phenomenon with dire and irreversible consequences, affecting different regions of the world. Assessment of spatial susceptibility to desertification requires long-term series of precipitation (P) and evapotranspiration (PET). An approach to desertification analysis is the use of spatially gridded time series of air temperature and precipitation, derived from spatial interpolation of in situ measurements and available globally. The aim of this article was to estimate the susceptibility to desertification over Southeast Brazil using monthly gridded data from the Global Precipitation Climatology Centre (GPCC), and from the Global Historical Climatology Network (GHCN). Two indices were used to estimate desertification susceptibility: the aridity index Ia (P/PET) and D (PET/P). Validation of these datasets was performed using in situ observations (1961—2010) from the National Institute of Meteorology (INMET) – (68 weather stations). Determination coefficient (r²) and the Willmott’s coefficient of agreement (d) between gridded and observed data revealed satisfactory accuracy and precision for grids of precipitation (r2 > 0.93, d > 0.90), air temperature (r2 > 0.94, d > 0.53) and PET (r2 > 0.93, d > 0.63). Areas susceptible to desertification were identified by the index Ia over the Northern regions of Minas Gerais and Rio de Janeiro states. No areas susceptible to desertification were identified using the index D. However, both indices indicated large areas of dry sub-humid climate, which can be strongly affected by drought conditions. Overall, climate gridded variables presented good precision and accuracy when used to identify areas susceptible to desertification.