For many years, rainfall has been measured in Brazil on a daily basis only; hence it is unusual to find studies considering a better temporal resolution for the whole country. However, since 2013, the National Centre for Monitoring and Early Warning of Natural Disasters (CEMADEN) has started to monitor rainfall in a sub hourly basis at more than 3,000 gauges. This study is the first to analyze sub-daily characteristics of rainfall in Brazil on national scale. Raw data from 3 years (2015-2017) was downloaded from CEMADEN’s home page and then quality control procedures were applied to select the high-quality rain gauges. Then, two rainfall properties were calculated: (i) Number of Wet Days – NWD, which is the number of rainy days per year; and (ii) Number of Effective Wet Days – NEWD, which is the number of rainy hours per year divided by 24 hours. Both NWD and NEWD were grouped according to NEWD values and spatially analyzed. About 1,100 rain gauges were used in this study: 824 (2015), 1,288 (2016), and 1,385 (2017). NWD ranges from 26 to 226 days (average: 151 days), while NEWD ranges from 1.2 to 47.8 days (average: 14.3 days). Results showed that group A (NEWD < 10.3 days) contains gauges located in the Brazilian Mid-western and northeastern semiarid regions. Group B (10.3 ≤ NEWD < 13.2 days) occurs in parts of the coastal region of Northeast and highlands of Southeast. Groups C (13.2 ≤ NEWD < 17.4 days) and D (NEWD ≥17.45 days) are found in South and part of the Southeastern coastal region. The region with the most concentrated rainfall rates (group A) is the one with the lowest annual rainfall. Orographic effects seem to cause reduction in NEWD, from 15.2 days to 11.8 days (group B). Groups C and D comprehend the rainiest region, preceded by the Amazon region. Finally, we highlight that spatial distribution of NWD and NEWD did not change abruptly annually, with an overall ratio between them of ~10 times. Although in some regions rainfall occurs in four months, it effectively falls from 10 to 13 days. This study is important to understand how concentrated the rainfall is in the different Brazilian regions.

Many remote sensing-based evapotranspiration (RSBET) algorithms have been proposed in the past decades and evaluated using flux tower data, mainly over North America and Europe. Model evaluation across South America has been done locally or using only a single algorithm at a time. Here, we provide the first evaluation of multiple RSBET models, at a daily scale, across a wide variety of biomes, climate zones, and land uses in South America. We used meteorological data from 25 flux towers to force four remote sensing based ET models: Priestley & Taylor Jet Propulsion Laboratory (PT-JPL), Global Land Evaporation Amsterdam Model (GLEAM), Penman-Monteith Mu model (PM-MOD), and Penman-Monteith Nagler model (PM-VI). ET was predicted satisfactorily by all four models, with correlations consistently higher (R²>0.6) for GLEAM and PT-JPL, and PM-MOD and PM-VI presenting overall better responses in terms of PBIAS (-10

Water scarcity is a key challenge to global development. In Brazil, the Sao Francisco River Basin (SFB) has experienced water scarcity problems because of decreasing streamflow and increasing demands from multiple sectors (e.g., food and energy production and urban supply). However, the drivers of decreased streamflow, particularly the potential role of groundwater withdrawals, have not been yet investigated. Here, we assess long-term trends in baseflow, quickflow, and streamflow of the SFB during 1980–2015 and constrain the most likely drivers of observed decreases through trend analysis of precipitation (P), evapotranspiration (ET), and terrestrial water storage change (TWS). We found that over 82% of the observed decrease in streamflow can be attributed to a significant decreasing baseflow trend (< -20 m3 s-1 y-1) along the SFR with spatial agreement between decreased baseflow, increased ET, and irrigated agricultural land. We also found a decrease in TWS across the SFB with trends exceeding -20 mm y-1. Overall, our findings indicate that decreasing groundwater contributions (i.e., baseflow) are the primary cause of the observed reduction in total SFR flow. A lack of significant climate trends indicates that climate variability likely has not caused the observed baseflow reduction, mainly in the Middle and Sub-middle SFB, and therefore groundwater and surface withdrawals may be the most likely driver of water scarcity over the SFB. We call for increased attention on groundwater’s key role for the SFB and integrated regional management of surface and groundwater.