Climate

Brazil is widely recognized as a global hotspot for flash drought, which sets in over weeks rather than a season, yet events are often reported under other names, among them wet-season dry spells, leaving the evidence unconsolidated. We reviewed 92 articles from 2012 to September 2024. From these, 23 of them were Brazil-focused events. Only five of those explicitly examined flash drought, and at least 35 definitions were in use across the reviewed set, hampering cross-study comparison and early warning; the North, Center-West and South remain underrepresented.

The Pantanal, the world’s largest tropical wetland, dried unusually over 2000-2021, with climate variability and land clearing in its headwaters both proposed as causes. Land-cover maps, gauged discharge and records of rainfall and evaporative demand back to 1951 were combined in a water balance analysis for the Upper Paraguay River Basin, reaching three decades further back than the land-cover record. We found that the runoff change across two wet and two dry periods, 96% traced to climate and only 4% to land cover, while wetland area shrank about 30% after 1985. The recent dry period was hotter and more arid than the 1965-1975 drought and may worsen rather than revert to humid conditions.

This study develops the version 2 of the Köppen-Geiger climate classification maps at 1-kilometer resolution from 1901 to 2099 and seven future climate pathways. We screened climate models by how plausibly they warm and dropping the least realistic, which narrows projected change and its spread. Roughly 5% of land outside Antarctica is shifited a major climate class since 1901-1930, and 5% to 13% more is projected by 2071-2099 depending on emissions scenario.

Farmers’ climate perceptions guide adaptation, but previsouly they have been tested against weather stations rather than soil moisture, which matters more for crops. We used surveys of 1,171 Zambian farm households after the 2016 harvest recalled onset dates for recent and earlier seasons. In our analysis each farmer’s own onset rule was compared with local rainfall and modeled soil moisture. Some 88% reported rains arriving 21.9 days later than a decade ago, yet the mean perceived onset for the latest season nearly matched the physically derived mean. Recall bias sets in as early as a year after harvest, and planting rules track maize planting dates, so policy should target current variability over future change.

Köppen-Geiger classifications, which categorize the world into cliamte types such as tropical, arid or polar, underpin ecology and climate impact work, but the global versions in wide use were drawn at about 10 kilometers or coarser resolution, without any uncertainty quantification. We developed new maps at about 1 kilometer for 1980-2016 by merging several precipitation and temperature datasets and quantifying its confidence value. A companion map projects 2071-2100 under a high-emissions scenario. Against 22,078 weather stations the new map classified 80.0% correctly, versus 66.1 to 73.4% for the earlier maps.

This study represents the most comprehensive global-scale precipitation dataset evaluation to date. We evaluated 13 uncorrected precipitation datasets using precipitation observations from 76 086 gauges, and 9 gauge-corrected ones using hydrological modeling for 9053 catchments. Our results highlight large differences in estimation accuracy, and hence, the importance of precipitation dataset selection in both research and operational applications.

A very strong El Niño was widely expected to ease the western United States drought in winter 2015/16, as in 1982/83 and 1997/98. Forecasts issued on 1 January 2016 covered winter precipitation and temperature and spring snowpack, from both empirical and dynamical methods. A common but poorly supported assumption, that anomalies scale with El Niño strength, was tested. Precipitation proved less sensitive to the signal than assumed. Only 46% of precipitation forecasts had the correct sign, against 87% for temperature and 67% for snowpack.