The South American low‐level jet (SALLJ) east of the Andes plays an important role in regional weather and hydrology by transporting large amounts of moisture from the Amazon to the subtropics. A new methodology is introduced for detecting SALLJ events based on seasonal‐percentile thresholds of wind speed and wind shear. Direct comparisons are made between new and conventional fixed‐threshold methods. Identification of SALLJ events is compared between five different reanalysis products and validated against available radiosonde observations. A new climatology of the SALLJ is presented for one particular reanalysis during a 38‐year period (1979–2016). Based on this new definition, the present study analyzes the spatiotemporal variability of the SALLJ on seasonal and interannual timescales, as well as trends in the jet over recent decades. Results show that the interannual variability of the jet's strength and frequency is significantly modulated by the El Niño Southern Oscillation, especially during spring. Trends in the vertically integrated moisture transport during SALLJ days reveal significant increases in the northwesterly moisture flux associated with the jet toward southern Brazil in spring, summer, and fall. These changes likely contribute to the increase in precipitation and extreme precipitation events observed over southeastern South America in recent decades.

Southeast Brazil (SE Brazil) is the most densely populated region in Brazil. Previous studies have shown evidence of positive trends in average precipitation and extreme events in a few locations, suggesting the increase in rainfall‐related hazards with potential impacts to urbanized areas of SE Brazil. This study provides a comprehensive analysis of the spatial variability of trends in extreme precipitation over SE Brazil focusing on regional and local scales. We examine two daily rainfall datasets with more than 70 years of data: individual stations and gridded observed precipitation data. Our results indicate that the frequency of both rainy days and extreme daily precipitation events have increased in Sao Paulo state. Conversely, precipitation has become more concentrated in fewer events in Rio de Janeiro and Espirito Santo states where both data sets indicate positive trends in the intensity of extreme daily rainfall. The increases in frequency and intensity of extreme events have both contributed to positive trends in total seasonal and average daily precipitation over Sao Paulo. Additionally, the individual stations indicate negative trends in the number of light rainy days over large urbanized areas in the state of Sao Paulo. The spatial patterns of trends indicate that they are influenced by the proximity of large urban centres and topographic features, and also suggest variations and changes in the major climatic systems affecting precipitation regimes over SE.

Fire is an integral component of ecosystems globally and a tool that humans have harnessed for millennia. Altered fire regimes are a fundamental cause and consequence of global change, impacting people and the biophysical systems on which they depend. As part of the newly emerging Anthropocene, marked by human-caused climate change and radical changes to ecosystems, fire danger is increasing, and fires are having increasingly devastating impacts on human health, infrastructure, and ecosystem services. Increasing fire danger is a vexing problem that requires deep transdisciplinary, trans-sector, and inclusive partnerships to address. Here, we outline barriers and opportunities in the next generation of fire science and provide guidance for investment in future research. We synthesize insights needed to better address the long-standing challenges of innovation across disciplines to (i) promote coordinated research efforts; (ii) embrace different ways of knowing and knowledge generation; (iii) promote exploration of fundamental science; (iv) capitalize on the “firehose” of data for societal benefit; and (v) integrate human and natural systems into models across multiple scales. Fire science is thus at a critical transitional moment. We need to shift from observation and modeled representations of varying components of climate, people, vegetation, and fire to more integrative and predictive approaches that support pathways toward mitigating and adapting to our increasingly flammable world, including the utilization of fire for human safety and benefit. Only through overcoming institutional silos and accessing knowledge across diverse communities can we effectively undertake research that improves outcomes in our more fiery future.

Climatic changes over the central Himalaya are critical for water resources in downstream regions where hundreds of millions of people live. Warming and drying in this region have both occurred in recent decades, but the associated meteorological factors are difficult to diagnose based on observations from unevenly distributed weather stations, reanalyses, and global climate models that poorly reproduce the orographic diurnal cycle. Here, recent trends in the summer diurnal cycle over the central Himalaya are investigated using a 36-year high-resolution dynamical downscaling. We illustrate contrasting trends over the diurnal cycle of circulation and convection over the Himalaya. In the daytime, warming of the slopes has enhanced anabatic upslope winds. At night, clearer skies have radiatively cooled the slopes, enhancing katabatic downslope winds. The enhanced upslope winds have prevented any drying over the mountains in the daytime, while the enhanced downslope winds are associated with significant nocturnal drying at high elevations. This amplification in the diurnal cycle is critical for projecting the future hydroclimate over the region’s complex terrain.