Attribution of Changes in Canadian Precipitation

Radley Horton,1,a Daniel Bader,1,a Yochanan Kushnir,2 Christopher Little,3 Reginald Blake,4 and Cynthia Rosenzweig5 1Columbia University Center for Climate Systems Research, New York, NY. 2Ocean and Climate Physics Department, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY. 3Atmospheric and Environmental Research, Lexington, MA. 4Physics Department, New York City College of Technology, CUNY, Brooklyn, NY. 5Climate Impacts Group, NASA Goddard Institute for Space Studies; Center for Climate Systems Research, Columbia University Earth Institute, New York, NY

In this study, future changes in precipitation extremes over 10 climatic regions in Canada and their mechanism under Representative Concentration Pathways (RCPs) throughout the 21st century are investigated by using the Providing Regional Climates for Impacts Studies (PRECIS) model. The performance of PRECIS in hindcasting total and extreme precipitation for the historical period is first evaluated through two experiments driven by the boundary conditions from both ERA‐Interim (1979–2011) and HadGEM2‐ES (1959–2005). The validation results indicate that PRECIS can reasonably reproduce both the magnitudes and spatial patterns of precipitation extremes over Canada. Changes in total and extreme precipitation for two future periods are analyzed to explore how regional climate over different climatic regions would respond to global warming. Mechanism governing changes in precipitation extremes is explored through a comprehensive analysis of potential climate factors and their correlations and interactions with precipitation extremes. There are obvious increasing trends over most regions for the magnitude of precipitation extremes except for the duration indices. Averages of projected precipitation extremes over the climatic regions in Canada are projected to increase under RCP4.5. Such increases under RCP8.5 would be amplified due to higher greenhouse gas emissions. The projected changes in total precipitation are dominated by changes in wind velocity and relative humidity (e.g., changes in horizontal water vapor flux that would have significant effects on the occurrence of precipitation in Canada). In addition, the changes in the majority of precipitation extremes are commonly attributed to the changes in the saturation vapor pressure due to warmer temperature as described by the Clausius‐Clapeyron equation.

The Northeastern United States has experienced a large increase in precipitation over recent decades. Annual and seasonal changes of total and extreme precipitation from station observations in the Northeast are assessed over multiple time periods spanning 1901-2014. Spatially averaged, both annual total and extreme precipitation across the Northeast have increased significantly since 1901, with changepoints occurring in 2002 and 1996, respectively. Annual extreme precipitation has experienced a larger increase than total precipitation; extreme precipitation from 1996-2014 was 53% higher than from 1901-1995. Spatially, coastal areas received more total and extreme precipitation on average, but increases across the changepoints are distributed fairly uniformly across the domain. Increases in annual total precipitation across the 2002 changepoint have been driven by significant total precipitation increases in fall and summer, while increases in annual extreme precipitation across the 1996 changepoint have been driven by significant extreme precipitation increases in fall and spring. The ability of gridded observed and reanalysis precipitation data to reproduce station observations was also evaluated. Gridded observations perform well in reproducing averages and trends of annual and seasonal total precipitation, but extreme precipitation trends show significantly different spatial and domain-averaged trends than station data. North American Regional Reanalysis generally underestimates annual and seasonal total and extreme precipitation means and trends relative to station observations, and also shows substantial differences in the spatial pattern of total and extreme precipitation trends within the Northeast.

This study examines future changes in precipitation over Northeast Asia and Korea using five regional climate model (RCM) simulations driven by single global climate model (GCM) under two representative concentration pathway (RCP) emission scenarios. Focusing on summer season (June–July–August) when heavy rains dominate in this region, future changes in precipitation and associated variables including temperature, moisture, and winds are analyzed by comparing future conditions (2071–2100) with a present climate (1981–2005). Physical mechanisms are examined by analyzing moisture flux convergence at 850 hPa level, which is found to have a close relationship to precipitation and by assessing contribution of thermodynamic effect (TH, moisture increase due to warming) and dynamic effect (DY, atmospheric circulation change) to changes in the moisture flux convergence. Overall background warming and moistening are projected over the Northeast Asia with a good inter-RCM agreement, indicating dominant influence of the driving GCM. Also, RCMs consistently project increases in the frequency of heavy rains and the intensification of extreme precipitation over South Korea. Analysis of moisture flux convergence reveals competing impacts between TH and DY. The TH effect contributes to the overall increases in mean precipitation over Northeast Asia and in extreme precipitation over South Korea, irrespective of models and scenarios. However, DY effect is found to induce local-scale precipitation decreases over the central part of the Korean Peninsula with large inter-RCM and inter-scenario differences. Composite analysis of daily anomaly synoptic patterns indicates that extreme precipitation events are mainly associated with the southwest to northeast evolution of large-scale low-pressure system in both present and future climates.

Previous studies have indicated a large model disagreement in the future projections of precipitation changes over the regions featuring Mediterranean climate. Many of these highly populated regions have been experiencing major droughts in the recent decades, raising concerns about future precipitation changes and their impacts. Here we investigate precipitation projections across five Mediterranean climate regions in the CMIP6 ensemble, and study their respective model agreements on the sign of future precipitation changes. We focus on the period 2050-2079 relative to 1970-1999, and consider two climate change scenarios (ssp2-4.5 and ssp5-8.5) over the Mediterranean Basin (MED), California (CAL), the central coast of Chile (SAA), the Cape Province area of South Africa (SAF) and southwest Australia (AUS).The CMIP6 ensemble mean suggests that annual mean cumulative precipitation will decrease over all the regions studied with the exception of northern California. In most cases, this decline is primarily attributed to a reduction in winter precipitation, except over the Mediterranean Basin, where the most significant decrease occurs in autumn. The model agreement on the sign of future precipitation changes is generally high over the regions and seasons where the ensemble mean indicates the precipitation decline in the future, and low over the regions showing the precipitation increase or no change. Specifically, the model agreement is low in southern California during all seasons, in northern Mediterranean during winter and autumn, and in southwest Australia during austral summer and autumn. CMIP6 ensemble means also indicate that the consecutive dry days (CDD) will increase in the future in all regions, but again the model agreement on this increase is low over southern and central California, the southern Mediterranean, and parts of southwest Australia. Similarly, the ensemble mean of consecutive wet days (CWD) indicate a decrease in all regions, with weak model agreement on the sign of future changes over CAL, northeast AUS and part of the MED region. The ensemble mean maximum one-day precipitation increases over all the regions, the most over the parts of southwest Australia and the Mediterranean.We conclude that despite substantial improvements to the new CMIP6 generation of models, the intermodel differences in future projections of precipitation changes continue to be high across parts of California, the Mediterranean Basin and southwest Australia. Impact studies need to account for these uncertainties and consider the whole intermodel range of projected precipitation changes.

Warming has already changed the patterns of precipitation and increased the risk of extreme climate events. An assessment of the influences from anthropogenic and natural forcings on future changes in precipitation is therefore essential to define appropriate mitigation and adaptation policies. We assess the effects of natural (NAT) and anthropogenic forcings (greenhouse gases [GHG] and anthropogenic aerosols [AA]) on precipitation over land areas simulated under the Coupled Model Intercomparison Project Phase 6 (CMIP6) SSP2‐4.5 scenario. Our results indicate that changes in precipitation due to GHG forcing, AA forcing and all external forcings (ALL) are projected to increase by about 3.0%–24.8%, 1.1%–6.9% and 4.2%–31.2%, respectively, across most land areas in the twenty‐first century, especially over the mid‐ and high latitudes of the Northern Hemisphere and central Africa, with an increase in the mean and flattening of the probability distribution functions (PDFs). By contrast, the NAT‐induced changes are relatively small, with a slight increase in the mean of the PDFs. The frequencies of both future extreme precipitation and dry events are projected to increase by 11%–101% and 3%–72%, respectively, over many continental regions under the influence of external forcings, especially under GHG forcing. Fingerprinting detection shows that the signals of GHG (except for Australia), AA and ALL forcing are detectable at the likely level (signal‐to‐noise ratio >0.95; 66% confidence) over most land areas. The GHG signals are stronger and detected earlier (after 2010s, likely level) than the AA signals (after 2060s, likely level).

Projected change in extreme rainfall events in China by the end of the 21st century using CMIP5 models

This study examines potential future changes of precipitation in China based on Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model projections for the medium (RCP4.5) and high (RCP8.5) emission scenarios. We first evaluate the biases of climate model output and correct the biases through quantile mapping. After bias correction, we examine the changes in mean precipitation as well as shifts in its frequency distribution. We also evaluate the changes in extreme precipitation based on frequency analysis techniques. Our results show that by the end of the century, mean precipitation is going to increase by 8% (12%) under RCP4.5 (RCP8.5) scenarios, resulted from a combination of an increase in precipitation intensity and a slight decrease in precipitation frequency. Spatially, precipitation is projected to increase more in northern China than southern China, and the increase is the least in the southeast. Seasonally, precipitation is projected to increase more in fall and winter, and less in spring and summer. The precipitation intensity distribution is likely to shift towards more heavy events, with a decrease in the contribution from light events and a significant increase in contribution from heavy events. Extreme precipitation is going to increase at much higher rates than mean precipitation, and the increase is more spatially uniform. Changes in annual and seasonal precipitation are closely linked with temperature change. Total precipitation increases at 2.6% (1.9%) per degree warming under RCP4.5 (RCP8.5), but extreme precipitation has much higher sensitivities ranging 4.5–6.5% per degree warming for events of various return intervals. The percentage increase per degree is generally smaller for RCP8.5 than RCP4.5 scenarios, suggesting a reduced sensitivity at higher temperature. In addition, the precipitation increase seems to be linked with changes in the atmospheric circulations that transport moisture in different regions in China. These changes have significant implications for the management of water resources and water‐related hazards.

The increasing impacts of climate change pose significant challenges for urban watersheds, necessitating effective strategies for stormwater management. This study evaluates the impacts of climate change on stormwater runoff and nutrient loads in the Sweetwater Creek Watershed, employing an integrated approach combining climate modeling, hydrological simulations, and green infrastructure (GI) optimization. Utilizing downscaled and bias-corrected data from eight General Circulation Models (GCMs) under two emission scenarios (SSP245 and SSP585), we project future changes in precipitation, temperature, and potential evapotranspiration (PET) for three timeframes: historical (1985–2014), near-future (2020–2049), and far-future (2070–2099). Projections indicate a 15%–25% increase in annual precipitation and a 2°C–4°C rise in average temperature under SSP245, with more extreme changes under SSP585, including up to a 40% increase in precipitation and a 5°C–7°C rise in temperature by the far-future period. These changes are expected to drive a 30%–45% increase in annual runoff volume and a 20%–35% rise in nutrient loads (e.g., nitrogen and phosphorus) under SSP585. The Storm Water Management Model (SWMM) was calibrated (NSE = 0.82) and validated (NSE = 0.79) using historical data to simulate hydrological processes and nutrient transport within the watershed. Using iPlantGreenS², a web-based GI planning tool, optimal GI locations and configurations were identified based on cost-effectiveness and nutrient removal efficiency. GI solutions, such as bioretention cells and vegetative swales, reduced runoff volume by 20%–35% and nutrient loads by 25%–40% in the near-future scenarios, with cost-effectiveness ratios ranging from $50–$150 per kilogram of nutrient removed. However, GI effectiveness declined by 10%–20% under extreme far-future climate conditions, emphasizing the need for adaptive designs to accommodate higher variability in precipitation and temperature. These findings highlight the critical role of GI in enhancing urban water management resilience and provide actionable insights for policymakers and urban planners.

Intensification of extreme precipitation in arid Central Asia

Characterizing precipitation seasonality and variability in the face of future uncertainty is important for a well-informed climate change adaptation strategy. Using the Colwell index of predictability and monthly normalized precipitation data from the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model ensembles, this study identifies spatial hotspots of changes in precipitation predictability in the United States under various climate scenarios. Over the historic period (1950–2005), the recurrent pattern of precipitation is highly predictable in the East and along the coastal Northwest, and is less so in the arid Southwest. Comparing the future (2040–2095) to the historic period, larger changes in precipitation predictability are observed under Representative Concentration Pathways (RCP) 8.5 than those under RCP 4.5. Finally, there are region-specific hotspots of future changes in precipitation predictability, and these hotspots often coincide with regions of little projected change in total precipitation, with exceptions along the wetter East and parts of the drier central West. Therefore, decision-makers are advised to not rely on future total precipitation as an indicator of water resources. Changes in precipitation predictability and the subsequent changes on seasonality and variability are equally, if not more, important factors to be included in future regional environmental assessment.

A stronger than global mean warming trend is projected over Central Asia in the coming century. Based on the historical simulations and projections under four combined scenarios of the Shared Socioeconomic Pathways and the Representative Concentration Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) provided by 15 models from the Sixth Phase of Coupled Model Intercomparison Project (CMIP6), we show a comprehensive picture of the future changes in precipitation over Central Asia under rapid warming and investigate possible mechanisms. At the end of the twenty-first century, robust increase of annual mean precipitation under all the scenarios is found (4.23 [2.60 to 7.36] %, 10.52 [5.05 to 13.36] %, 14.51 [8.11 to 16.91] %, 14.41 [9.58 to 21.26] % relative to the present-day for SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5, respectively). The response of precipitation to increasing global mean temperature shows similar spatial patterns for the four scenarios with stronger changes over Tianshan mountain and the northern part of Central Asia. Further analysis reveals a wetting trend in spring and a drying trend in summer in both the north of Central Asia (NCA) and south of Central Asia (SCA). The wetting trend in spring is balanced by the increase of evaporation, while the drying trend in summer is mainly contributed by the decrease of vertical moisture advection. The thermodynamic effects associated with humidity changes contribute to the drying trends in both the two domains, while the dynamic effects favor for the drying trend in NCA and offset the drying trend in SCA. The response of precipitation to increasing temperature results in enhanced seasonalities for SCA and NCA, and an advancing of the first peak from summer to spring in the NCA.

The warming of the planet and ongoing climate change are now a scientifically proven fact. These phenomena have an impact on nature and many human activities, but logically affect agriculture the most. History has confirmed that the production of grapes (the extent and quality) is significantly affected by climate change. The main goal of this study was to evaluate the impact of climate change through changes in average precipitation and average temperatures on the quantity of grape production in the Czech Republic. A partial goal was then to predict the future development of grape production depending on the expected total precipitation and average temperatures. The effect of changes in average temperatures and total precipitation was evaluated using multiple linear regression methods. The multiple regression model did not reveal a dependence of the total precipitation and average temperatures on the development of the value of vine production due to the statistical insignificance of the effect of average temperatures on the value of vine production. However, when abstracting the effect of average temperatures on the value of vine production, the research confirmed the effect of the change in total precipitation on the value of vine production. The analysis identified the effect of changes in total precipitation and temperatures on the production of grapes in the Czech Republic.

In China, summer precipitation contributes a major part of the total precipitation amount in a year and has major impacts on society and human life. Whether any changes in summer precipitation are affected by external forcing on the climate system is an important issue. In this study, an optimal fingerprinting method was used to compare the observed changes of total, heavy, moderate, and light precipitation in summer derived from newly homogenized observation data with the simulations from multiple climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The results demonstrate that the anthropogenic forcing signal can be detected and separated from the natural forcing signal in the observed increase of seasonal accumulated precipitation amount for heavy precipitation in summer in China and eastern China (EC). The simulated changes in heavy precipitation are generally consistent with observed change in China but are underestimated in EC. When the changes in precipitation of different intensities are considered simultaneously, the human influence on simultaneous changes in moderate and light precipitation can be detected in China and EC in summer. Changes attributable to anthropogenic forcing explain most of the observed regional changes for all categories of summer precipitation, and natural forcing contributes little. In the future, with increasing anthropogenic influence, the attribution-constrained projection suggests that heavy precipitation in summer will increase more than that from the model raw outputs. Society may therefore face a higher risk of heavy precipitation in the future.

We present the climate change impact on the annual and seasonal precipitation over Rajang River Basin (RRB) in Sarawak by employing a set of models from Coupled Model Intercomparison Project Phase 5 (CMIP5). Based on the capability to simulate the historical precipitation, we selected the three most suitable GCMs (i.e. ACCESS1.0, ACCESS1.3, and GFDL-ESM2M) and their mean ensemble (B3MMM) was used to project the future precipitation over the RRB. Historical (1976–2005) and future (2011–2100) precipitation ensembles of B3MMM were used to perturb the stochastically generated future precipitation over 25 rainfall stations in the river basin. The B3MMM exhibited a significant increase in precipitation during 2080s, up to 12 and 8% increase in annual precipitation over upper and lower RRB, respectively, under RCP8.5, and up to 7% increase in annual precipitation under RCP4.5. On the seasonal scale, Mann-Kendal trend test estimated statistically significant positive trend in the future precipitation during all seasons; except September to November when we only noted significant positive trend for the lower RRB under RCP4.5. Overall, at the end of the twenty-first century, an increase in annual precipitation is noteworthy in the whole RRB, with 7 and 10% increase in annual precipitation under the RCP4.5 and the RCP8.5, respectively.