Special issue  

Extensive, long-standing dry and wet episodes are frequent climatic extreme events (EEs) in the Iberian Peninsula (IP). A method for ranking regional extremes of persistent, widespread drought and wet events is presented, using different SPEI timescales. Results show that there is no region more prone to EE occurrences in the IP, the most extreme extensive agricultural droughts evolve into hydrological and more persistent extreme droughts, and widespread wet and dry EEs are anti-correlated.

By analysing old wind direction observations taken aboard sailing ships, it has been possible to build an index quantifying the moisture transport from the equatorial Pacific into large areas of Central America and northern South America starting in the late 19th century. This transport is deeply related to a low-level jet known as the Choco jet. Our results suggest that the seasonal distribution of the precipitation associated with this transport could have changed over the time.

Ice melting at the scale of inter-annual fluctuations against the trend is favoured by an increase in moisture transport in summer, autumn, and winter and a decrease in spring. On a daily basis extreme humidity transport increases the formation of ice in winter and decreases it in spring, summer, and autumn; in these three seasons it thus contributes to Arctic sea ice melting. These patterns differ sharply from that linked to decline, especially in summer when the opposite trend applies.

We analyse moisture transport triggered by the Great Plains low-level jet (GPLLJ), a maximum in wind speed fields located within the first kilometre of the US Great Plain's troposphere, through the innovative Eulerian Weather Research and Forecasting Model tracer tool. Much moisture associated with this low-level jet has been found in northern regions located in a vast extension of the continent, highlighting the key role played by the GPLLJ in North America's advective transport of moisture.

The identification of moisture sources for a region is of prominent importance regarding the characterization of precipitation. In this work, the moisture sources for the western North American monsoon (WNAM) region are identified; these sources are the Gulf of California, the WNAM itself, eastern Mexico and the Caribbean Sea. We find that rainfall intensity over the WNAM region is related to the amount of moisture transported from the Caribbean Sea and eastern Mexico during the preceding days.

We analyzed changes in surface relative humidity (RH) at the global scale from 1979 to 2014 and compared the variability and trends in RH with those in land evapotranspiration and ocean evaporation in moisture source areas across a range of selected regions worldwide. Our results stress that the different hypotheses that may explain the decrease in RH under a global warming scenario could act together to explain recent RH trends.

We have identified changes in the pattern of moisture transport for precipitation over the Arctic region, the Arctic Ocean, and its 13 main subdomains concurrent with the major sea ice decline that occurred in 2003. The pattern consists of a general decrease in moisture transport in summer and enhanced moisture transport in autumn and early winter, with different contributions depending on the moisture source and ocean subregion.

Atmospheric rivers (ARs) account for most of the extreme flooding events on the northwestern coast of the US. In a warmer climate, ARs in this region are projected to become more frequent and intense. We present an integrated modeling system to quantify atmospheric–hydrologic–hydraulic and economic impacts of an AR event in western Washington. Our integrated modeling tool provides communities in the region with a range of possible future physical and economic impacts associated with AR flooding.

We present here a newly implemented water vapor tracer tool into the WRF meteorological model (WRF-WVT). A detailed validation shows high accuracy, with an error of much less than 1 % in moisture traceability. As an example application, we show that for the 2014 Great Lake-effect snowstorm, above 30 % of precipitation in the regions immediately downwind originated from lake evaporation, with contributions exceeding 50 % in the areas with highest snowfall accumulations.

This paper analyses the potential role of atmospheric rivers in the explosive cyclone deepening. Using ERA-Interim reanalysis data for 1979–2011, we analyse the concurrence of atmospheric rivers and explosive cyclogenesis over the North Atlantic and North Pacific basins for the extended winter months (ONDJFM).

This paper analyzes the origin of the moisture in two extremely important atmospheric river (and extreme precipitation) events. The distribution of the moisture with regard to the low-level jet is analyzed as well, and the classic association of the atmospheric river to the former is discussed.

For the first time, a climatology of Lyapunov exponents (FTLE) for the period 1979–2014 has been established. This climatology is able to reproduce the main large-scale structures observed in the troposphere. The mean FTLE has been shown to correlate with the baroclinic Eady growth rate within timescales of a few days. As a case study, the contribution of atmospheric rivers to this climatology and their contribution to rainfalls over the Sahara and UK regions have been studied.

This work aims to leverage the understanding of precipitation distribution with a long-term analysis of moisture transport from oceanic and continental sources and its relevance for regional precipitation features, variability and trends. Combining reanalysis, model output, in situ observations and satellite products we provide a robust survey that is useful for, for example, modelling, water resource management, flood and drought monitoring, rain-linked disease spread and ecosystem studies.