Widening of the tropical belt in a changing climate

Nature Portfolio (Springer Nature) | December 2nd, 2007

Some of the earliest unequivocal signs of climate change have been the warming of the air and ocean, thawing of land and melting of ice in the Arctic. But recent studies

Some of the earliest unequivocal signs of climate change have been the warming of the air and ocean, thawing of land and melting of ice in the Arctic. But recent studies are showing that the tropics are also changing. Several lines of evidence show that over the past few decades the tropical belt has expanded. This expansion has potentially important implications for subtropical societies and may lead to profound changes in the global climate system. Most importantly, poleward movement of large-scale atmospheric circulation systems, such as jet streams and storm tracks, could result in shifts in precipitation patterns affecting natural ecosystems, agriculture, and water resources. The implications of the expansion for stratospheric circulation and the distribution of ozone in the atmosphere are as yet poorly understood. The observed recent rate of expansion is greater than climate model projections of expansion over the twenty-first century, which suggests that there is still much to be learned about this aspect of global climate change.

Winter melt trends portend widespread declines in snow water resources

Nature Portfolio (Springer Nature) | April 5th, 2021

In many mountainous regions, winter precipitation accumulates as snow that melts in the spring and summer, which provides water to one billion people globally. Climate wa

In many mountainous regions, winter precipitation accumulates as snow that melts in the spring and summer, which provides water to one billion people globally. Climate warming and earlier snowmelt compromise this natural water storage. Although snowpack trend analyses commonly focus on the snow water equivalent (SWE), we propose that trends in the accumulation season snowmelt serve as a critical indicator of hydrological change. Here we compare long-term changes in the snowmelt and SWE from snow monitoring stations in western North America and find 34% of stations exhibit increasing winter snowmelt trends (P < 0.05), a factor of three larger than the 11% showing SWE declines (P < 0.05). Snowmelt trends are highly sensitive to temperature and an underlying warming signal, whereas SWE trends are more sensitive to precipitation variability. Thus, continental-scale snow water resources are in steeper decline than inferred from SWE trends alone. More winter snowmelt will complicate future water resource planning and management.

Workshop on Improving Sub-Seasonal and Seasonal Precipitation Forecasting for Drought Preparedness

California Department of Water Resources (DWR) | October 15th, 2015

Skillful sub-seasonal (monthly) to seasonal (the water year) precipitation forecasting would support many facets of water management, providing lead time for preparing fo

Skillful sub-seasonal (monthly) to seasonal (the water year) precipitation forecasting would support many facets of water management, providing lead time for preparing for extreme events and allowing for more efficient operation of water infrastructure. Current forecast practices and scientific capabilities for making skillful forecasts beyond the weather time domain, however, are limited. Through a series of prior annual workshops on climate variability, climate extremes, and drought held by the Council and the California Department of Water Resources (CDWR), some possible opportunities for improving forecasting skill at a regional scale have been identified. The purpose of this May 2015 workshop was to develop a Western vision for improving monthly and seasonal precipitation forecasting, loosely modeled after the Council’s vision for an observing network for Western extreme precipitation. The analyses performed to understand patterns responsible for heavy precipitation events at a regional scale – such as atmospheric river storms or the Southwest monsoon -- also point out pathways to explore for improving forecasting of these events. The timing is ripe for efforts to improve monthly and seasonal forecasting. Drought in the West has called attention to the need for better information to support preparedness and response, and NOAA’s report on the California drought provides a focal point for followup actions. The National Weather Service (NWS) is reviewing approaches for developing experimental week three and week four outlooks. The National Research Council has convened a committee to develop a U.S. research agenda to advance subseasonal to seasonal forecasting.