The MexHiResClimDB and the MexWatDB: Two new country-wide databases in Mexico to improve hydrological modelling from regional to local scales.

This work presents two country-wide datasets for Mexico: (1) Mexico's High Resolution Climate Database (MexHiResClimDB) and (2) Mexico's watershed database (MexWatDB). The MexHiResClimDB is a long-term (1951-2020) climate database at a spatial resolution of approximately 600 metres (that comprises daily minimum, average and maximum temperature as well as precipitation), while the MexWatDB is a new watershed classification for Mexico based on the Pfafstetter classification system. This new classification system is proposed because the currently used watershed classification in Mexico was developed in the 1950s (and is based on letters without a logical sequence, i.e. no upstream or downstream criteria was used for its coding). The MexWatDB consists of three nested watershed levels: the first division (L₁) comprises 359 watersheds, while L₂ has 1980 watersheds and L₃ a total of 6262 hierarchically ordered watersheds (whereas the currently used scheme has a total of 976). While the MexHiresClimDB comprises daily, monthly and yearly rasters of T_min, T_avg, T_max and Precip (with their corresponding normals for the 1951-1980, 1961-1990, 1971-2000, 1981-2010 and 1991-2020 periods), the MexWatDB includes the aforementioned variables with the previously mentioned temporal aggregation on a watershed basis for each division level (i.e, L₁, L₂ and L₃). An adequate watershed classification and a high resolution climate database is needed in Mexico, because daily precipitation can vary from 0 to more than 300 mm per day (or more than fivefold on a monthly basis for adjacent watersheds). These two new databases will be helpful to develop hydrological models from regional to local scales and to quantify the spatial variability of climate change in Mexico.