Future change in extreme precipitation in East Asian spring and Mei-yu seasons in two high-resolution AGCMs

Precipitation in the spring and Mei-yu seasons, the main planting and growing period in East Asia, is crucial to water resource management. Changes in spring and Mei-yu extreme precipitation under global warming are evaluated based on two sets of high-resolution simulations with various warming pattern of sea surface temperature (SST'spa). In the spring season, extreme precipitation exhibits larger enhancements over the northern flank of the present-day prevailing rainy region and a tendency of increased occurrence and enhanced intensity in the probability distribution. These changes imply a northward extension of future spring rainband. Although the mean precipitation shows minor change, enhanced precipitation intensity, less total rainfall occurrence, and prolonged consecutive dry days suggest a more challenging water resource management in the warmer climate. The projected enhancement in precipitation intensity is robust compared with the internal variability related to initial conditions (σˆint) and the uncertainty caused by SST'spa (σˆΔSST). In the Mei-yu season, extreme precipitation strengthens and becomes more frequent over the present-day prevailing rainband region. The thermodynamic component of moisture flux predominantly contributes to the changes in the spring season. In the Mei-yu season, both the thermodynamic and dynamic components of moisture flux enhance the moisture transport and intensify the extreme precipitation from southern China to northeast Asia. Compared with spring season, projecting future Mei-yu precipitation is more challenging because of its higher uncertainty associated with 1) the σˆint and σˆΔSST embedded in the projections and 2) the model characteristics of present-day climatology that determines the spatial distribution of precipitation enhancement.publishedVersio

Northern Hemisphere Urban Heat Stress and Associated Labor Hour Hazard from ERA5 Reanalysis

Increasing surface air temperature is a fundamental characteristic of a warming world. Rising temperatures have potential impacts on human health through heat stress. One heat stress metric is the wet-bulb globe temperature, which takes into consideration the effects of radiation, humidity, and wind speed. It also has broad health and environmental implications. This study presents wet-bulb globe temperatures calculated from the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis and combines it with health guidelines to assess heat stress variability and the potential for reduction in labor hours over the past decade on both the continental and urban scale. Compared to 2010–2014, there was a general increase in heat stress during the period from 2015 to 2019 throughout the northern hemisphere, with the largest warming found in tropical regions, especially in the northern part of the Indian Peninsula. On the urban scale, our results suggest that heat stress might have led to a reduction in labor hours by up to ~20% in some Asian cities subject to work–rest regulations. Extremes in heat stress can be explained by changes in radiation and circulation. The resultant threat is highest in developing countries in tropical areas where workers often have limited legal protection and healthcare. The effect of heat stress exposure is therefore a collective challenge with environmental, economic, and social implications.publishedVersio

NorCPM1 and its contribution to CMIP6 DCPP

The Norwegian Climate Prediction Model version 1 (NorCPM1) is a new research tool for performing climate reanalyses and seasonal-to-decadal climate predictions. It combines the Norwegian Earth System Model version 1 (NorESM1) – which features interactive aerosol-cloud schemes and an isopycnic-coordinate ocean component with biogeochemistry – with anomaly assimilation of SST and T/S-profile observations using the Ensemble Kalman Filter (EnKF).publishedVersio

Contrasting Various Metrics for Measuring Tropical Cyclone Activity

Popular metrics used for measuring the tropical cyclone (TC) activity, including NTC (number of tropical cyclones), TCD (tropical cyclone days), ACE (accumulated cyclone energy), PDI (power dissipation index), along with two newly proposed indices: RACE (revised accumulated cyclone energy) and RPDI (revised power dissipation index), are compared using the JTWC (Joint Typhoon Warning Center) best-track data of TC over the western North Pacific basin. Our study shows that, while the above metrics have demonstrated various degrees of discrepancies, but in practical terms, they are all able to produce meaningful temporal and spatial changes in response to climate variability. Compared with the conventional ACE and PDI, RACE and RPDI seem to provide a more precise estimate of the total TC activity, especially in projecting the upswing trend of TC activity over the past few decades, simply because of a better approach in estimating TC wind energy. However, we would argue that there is still no need to find a ¡§universal¡¨ or ¡§best¡¨ metric for TC activity because different metrics are designed to stratify different aspects of TC activity, and whether the selected metric is appropriate or not should be determined solely by the purpose of study. Except for magnitude difference, the analysis results seem insensitive to the choice of the best-track datasets

Evaluating the Emanuel-Nolan genesis potential index: Contrast between North Atlantic and western North Pacific

Tropical cyclone (TC) activity during the period from 1979 - 2010 represented by the Emanuel-Nolan “genesis potential index” (EN-GPI) is compared and evaluated against observation of TC records over the North Atlantic and the western North Pacific. This study shows that, while the EN-GPI might be a nice proxy in reproducing major climatic features of TC activity (e.g., spatial genesis pattern and seasonal cycle), its performance in representing the interannual TC variability appears to be highly basin-dependent, with a skillful performance over the North Atlantic, but not over the western North Pacific. A term budget analysis of the EN-GPI, along with a number of designed sensitivity experiments, clearly points out that such a huge performance contrast between the two ocean basins must come from a spurious estimation of the “maximum potential intensity” (Vpot) term over the western North Pacific for its magnitude being too sensitive to change of SST compared with that over the North Atlantic. A refinement of the EN-GPI according to regional climate conditions is advised to projecting the long-term TC activity, in particular, over the western North Pacific

Future change in extreme precipitation in East Asian spring and Mei-yu seasons in two high-resolution AGCMs

Precipitation in the spring and Mei-yu seasons, the main planting and growing period in East Asia, is crucial to water resource management. Changes in spring and Mei-yu extreme precipitation under global warming are evaluated based on two sets of high-resolution simulations with various warming pattern of sea surface temperature (SST'spa). In the spring season, extreme precipitation exhibits larger enhancements over the northern flank of the present-day prevailing rainy region and a tendency of increased occurrence and enhanced intensity in the probability distribution. These changes imply a northward extension of future spring rainband. Although the mean precipitation shows minor change, enhanced precipitation intensity, less total rainfall occurrence, and prolonged consecutive dry days suggest a more challenging water resource management in the warmer climate. The projected enhancement in precipitation intensity is robust compared with the internal variability related to initial conditions (σˆint) and the uncertainty caused by SST'spa (σˆΔSST). In the Mei-yu season, extreme precipitation strengthens and becomes more frequent over the present-day prevailing rainband region. The thermodynamic component of moisture flux predominantly contributes to the changes in the spring season. In the Mei-yu season, both the thermodynamic and dynamic components of moisture flux enhance the moisture transport and intensify the extreme precipitation from southern China to northeast Asia. Compared with spring season, projecting future Mei-yu precipitation is more challenging because of its higher uncertainty associated with 1) the σˆint and σˆΔSST embedded in the projections and 2) the model characteristics of present-day climatology that determines the spatial distribution of precipitation enhancement

Northern Hemisphere Urban Heat Stress and Associated Labor Hour Hazard from ERA5 Reanalysis

Increasing surface air temperature is a fundamental characteristic of a warming world. Rising temperatures have potential impacts on human health through heat stress. One heat stress metric is the wet-bulb globe temperature, which takes into consideration the effects of radiation, humidity, and wind speed. It also has broad health and environmental implications. This study presents wet-bulb globe temperatures calculated from the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis and combines it with health guidelines to assess heat stress variability and the potential for reduction in labor hours over the past decade on both the continental and urban scale. Compared to 2010–2014, there was a general increase in heat stress during the period from 2015 to 2019 throughout the northern hemisphere, with the largest warming found in tropical regions, especially in the northern part of the Indian Peninsula. On the urban scale, our results suggest that heat stress might have led to a reduction in labor hours by up to ~20% in some Asian cities subject to work–rest regulations. Extremes in heat stress can be explained by changes in radiation and circulation. The resultant threat is highest in developing countries in tropical areas where workers often have limited legal protection and healthcare. The effect of heat stress exposure is therefore a collective challenge with environmental, economic, and social implications

NorCPM1 and its contribution to CMIP6 DCPP

The Norwegian Climate Prediction Model version 1 (NorCPM1) is a new research tool for performing climate reanalyses and seasonal-to-decadal climate predictions. It combines the Norwegian Earth System Model version 1 (NorESM1) – which features interactive aerosol-cloud schemes and an isopycnic-coordinate ocean component with biogeochemistry – with anomaly assimilation of SST and T/S-profile observations using the Ensemble Kalman Filter (EnKF)