Simple Daily Intensity Index Research Articles

Sub-Daily Rainfall Intensity Extremes: Evaluating Suitable Indices at Australian Arid and Wet Tropical Observing Sites

Rainfall intensity extremes are relevant to many aspects of climatology, climate change, and landsurface processes. Intensity is described and analysed using a diversity of approaches, reflecting its importance in these diverse areas. The characteristics of short-interval intensity extremes, such as the maximum 5-min intensity, are explored here. It is shown that such indices may have marked diurnal cycles, as well as seasonal variability. Some indices of intensity, such as the SDII (simple daily intensity index), provide too little information for application to landsurface processes. Upper percentiles of the intensity distribution, such as the 95th and 99th percentiles (Q95 and Q99) are used as indices of extreme intensity, but problematically are affected by changes in intensity below the nominated threshold, as well as above it, making the detection of secular change, and application to sites with contrasting rainfall character, challenging. For application to landsurface processes, a new index is introduced. This index (RQ95), is that intensity or rainfall rate above which 5% of the total rainfall is delivered. This index better reflects intense rainfall than does Q95 of even 5-min accumulation duration (AD) rainfall depths. Such an index is helpful for detecting secular change at an observing station, but, like Q95, remains susceptible to the effects of change elsewhere in the distribution of intensities. For understanding impacts of climate and climate change on landsurface processes, it is argued that more inclusive indices of intensity are required, including fixed intensity criteria.

Modeling of the saffron yield in Central Khorasan region based on meteorological extreme events

In the current research, influences of climate extreme indices on saffron yield were studied. To evaluate the trend of extreme climate indices (1991–2015), 27 indices of rainfall and temperature, recommended by the Expert Team for Climate Change Detection Monitoring were used for some synoptic stations in the North East of Iran. Afterward, using the stepwise regression analysis, the effects of climate extreme indices were evaluated. Then, by selecting the best indices, a saffron yield model was proposed. The model accuracy was monitored and evaluated using indices of R Squared (R2, 0.68), Root Mean Square Error (RMSE, 0.6), and Normalized Root Mean Square Error (NRMSE, 14) indicating that the model has a high efficiency. Also, the accuracy of the model was acceptable. The best indices were selected and the model of yield–climate extreme indices was presented. The model verification was performed using Relative Deviation (RD, 9.5%). The modeling showed that indices of summer days, the number of tropical nights, maximum monthly daily minimum temperature, the index of cool nights, the minimum and maximum monthly daily maximum, annual precipitation on wet days, and simple daily intensity index are the most effective climate extreme indices on saffron yield. Analysis of indices in the study area showed that the thermal and precipitation extreme indices had significant changes. Therefore, the cold extreme indices had a decreasing trend while the hot extreme indices showed a strong increasing trend. Furthermore, extreme precipitation indices also had decreasing trends. Considering these results, it can be concluded that the incremental trend of warming extreme indices coupled with the decremental trend of extreme precipitation indices are the most significant factors in the reduction of saffron yield.

Projected changes in extreme precipitation events over China in the 21st century using PRECIS

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 79:91-107 (2019) - DOI: https://doi.org/10.3354/cr01576 Projected changes in extreme precipitation events over China in the 21st century using PRECIS Yujing Zhang1, Liang Fu2, Chunchun Meng3, Lei Zhang3, Yinlong Xu3,* 1Hangzhou Meteorological Bureau, Hangzhou 310051, PR China 2Zhejiang Meteorological Observatory, Hangzhou 310018, PR China 3Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, PR China *Corresponding author: xuyinlong@caas.cn ABSTRACT: This study evaluates possible spatial and temporal changes in precipitation extremes over China under Representative Concentration Pathway (RCP) scenarios using the regional climate model system ‘Provide Regional Climates for Impacts Studies’ (PRECIS), driven with HadGEM2-ES. The extreme precipitation indices applied are consecutive dry days (CDDs), simple daily precipitation intensity index (SDII), maximum consecutive 5 d precipitation (RX5D) and total precipitation amount on extremely wet days (R95P). PRECIS can satisfactorily reproduce the spatial distribution of extreme precipitation indices compared to the observed data. By the end of the 21st century, CDD and SDII are projected to increase under all RCP scenarios in southern China, and R95P and RX5D are projected to increase under RCP4.5 and RCP8.5 scenarios, which indicates the possible increasing risks of prolonged dry spells and heightened floods in these regions. In northern China, CDDs are expected to decrease, while other indices are expected to increase in the future, implying a decrease in the risk of prolonged drought periods and an increase in flood risk; this pattern is most prominent over northwestern China. For the temporal evolution of the extreme precipitation indices, the change rates are most significant under the RCP8.5 scenario. Compared to present-day levels, from low to high emission scenarios, CDDs would decrease by ~1-10%, SDII would increase by ~6-14%, R95P would increase by ~9-21%, and RX5D would increase by ~6-26%, respectively, suggesting that dry extremes would be alleviated, while wet extremes would become more pronounced in general over China toward the end of the 21st century. KEY WORDS: Extreme precipitation events · China · Representative Concentration Pathway · Climate change · PRECIS Full text in pdf format Correction NextCite this article as: Zhang Y, Fu L, Meng C, Zhang L, Xu Y (2019) Projected changes in extreme precipitation events over China in the 21st century using PRECIS. Clim Res 79:91-107. https://doi.org/10.3354/cr01576 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 79, No. 2. Online publication date: November 14, 2019 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2019 Inter-Research.

Observed trends in daily extreme precipitation indices in Aguascalientes, Mexico

AbstractPrecipitation and its distribution greatly influence the evolution of ecosystems and the development of society. The objective was to analyse trends in extreme precipitation indices at 25 weather stations of Aguascalientes State. Eleven extreme precipitation indices were obtained. The time series of these indices were analysed with the non‐parametric Mann–Kendall test. The number of days above 50 mm, consecutive wet days, and extremely wet days did not have significant trends at any of the weather stations. Each of the indices maximum 1 day precipitation amount, maximum 5 day precipitation amount and number of very heavy precipitation days showed a significant positive trend at 12% of the weather stations; both the number of heavy precipitation days and the number of very wet days had significant positive trends at 8% of the weather stations; the simple daily intensity index, consecutive dry days and annual total wet‐day precipitation showed significant positive trends at 20%, 36% and 4% of weather stations, respectively. The intensity index was the only one that showed a significant negative trend, which happened at 4% of the weather stations. In a small part of Aguascalientes, the precipitation intensity, the number of rainy days and the accumulated total increased in short periods. Also, in a reduced region, daily precipitation intensity decreased; and in another very small area the number of dry days increased. For mitigating the effects of these phenomena, it is suggested that water be used more efficiently for sustained agricultural production systems and ecosystem management. The results of the present study will be of great importance in future economic planning in the Aguascalientes State.

Spatiotemporal Variations of Extreme Precipitation and Study on Chaotic Characteristics in the Xijiang River Basin, China

Climate change leads to the increase of frequency and intensity for extreme precipitation events, potentially threatening the development of our society. It is of great significance to study the spatiotemporal variation of precipitation for understanding cycle process of water and its response to global warming. This paper selects the Xijiang River basin, which locates on a low latitude and coastland, as the research area. The spatiotemporal distribution and homogeneity of precipitation are analyzed, and the spatial trend is studied using 12 extreme precipitation indices. Finally, chaotic characteristics are evaluated for daily precipitation. The results showed that the precipitation in the basin tended to be unevenly distributed. On wet days, precipitation in the middle and the west was more and more uniform. The proportion of tiny rain was the largest, between 33.5% and 41.3%. The proportion of violent rain was the smallest, between 0.1% and 4.7%. Duan had the highest frequency for violent rain, and the probability of disasters caused by extreme precipitation near the station was the highest. The simple daily intensity index (SDII) showed a significant increase in the middle and the northeast. PRCPTOT (annual total wet-day precipitation) showed a decreasing trend in the northwest. The average rates of variation for R95PTOT (precipitation on very wet days) and R99PTOT (precipitation on extremely wet days) were −0.01 mm/year and 0.06 mm/year, respectively. There might be a risk of drought on the west of the basin in the future. Precipitation in other locations was still relatively abundant. Daily precipitation showed high dimension and high chaotic characteristics. The MED (minimum embedding dimension) was between 11 and 30, and the MLE (largest Lyapunov exponent) was between 0.037 and 0.144.

Projected changes in extreme precipitation events over various subdivisions of India using RegCM4

Present study attempts to project extreme precipitation indices over 34 different meteorological subdivisions and six homogeneous regions such as Northwest, Central Northeast, Northeast, West Central, Peninsular India and Hilly Region during summer monsoon season in the twenty-first century. For this purpose, the Regional Climate Model version4 (RegCM4) had been run at 50 km horizontal resolution forced with the global model GFDL-ESM2 M, during reference period 1976–2005 for the model validation, and the mid- (2031–2060) and far-future (2070–2099) for projections under RCP8.5 scenario over the South Asia CORDEX domain. In this paper, model simulated precipitation has been validated against IMD, APHRODITE and NCEP/NCAR data sets. The results indicate that RegCM4 captures the important features of seasonal precipitation and various extreme indices over the study area. The RegCM4 has projected an increase in the mean seasonal precipitation by 0.56 mm/day whereas in case of GFDL model the rate is 0.39 mm/day during the far-future relative to the reference period. The heavy precipitation indices are projected to increase more frequently (0.264/decade) than the mean precipitation rate (0.01/decade) over India. The correlations between the extreme precipitation indices and the seasonal mean precipitation are found to be strong. In addition, the consecutive dry days are projected to occur more frequently (3–5 days) over West Central (Telangana, Vidarbha and Marathwada) and west Rajasthan while consecutive wet days are projected to decrease over larger parts of India during far-future. Similarly, 1 day maximum precipitation and the simple daily intensity index are projected to increase consistently from mid- to far- futures over some sub-divisions of West coast, Hilly and Northeast regions. From a spatial probability perspective, model projection indicates more frequent severe drought and flood conditions over India.

Inter-Seasonal Precipitation Variability over Southern China Associated with Commingling Effect of Indian Ocean Dipole and El Niño

This study analyzed temporal and regional responses of precipitation to the Indian Ocean Dipole (IOD) over southern China and the differences between IOD-only and El Niño–southern oscillation–IOD cases. The Mann–Kendall test and intentionally biased bootstrapping were used. The results revealed three main phases (development and peak, decay, and aftermath) of percentage changes in seasonal total rainfall and showed the most positive sensitivity to positive IOD events in southern China. Moreover, El Niño played an essential role in intensifying the positive response to positive IOD events in the first and second phases while contributing little to the third. In terms of precipitation variability (frequency, intensity, and magnitude), seasonal maximum 1-day precipitation and maximum number of consecutive dry days were more sensitive to positive IOD events than the maximum number of consecutive wet days and simple daily precipitation intensity index. This study enhances knowledge of the temporal and spatial sensitivity of precipitation features to positive IOD events over southern China.

Historical and future projected frequency of extreme precipitation indicators using the optimized cumulative distribution functions in China

The cumulative distribution functions (CDFs) of extreme precipitation indices (EPIs) characterize the occurrence of extreme precipitation events, but some CDFs have been either exaggerated or underestimated. In this study, we selected the most suitable CDFs from ten commonly used functions (i.e., Normal, two- and three-parameter log-normal, extreme value type-I, generalized extreme value-GEV, Weibull, two-parameter Gamma, Pearson-III type, Poisson, and Pareto) for the site- and regional-specific EPIs in China and projected their changes under the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios combined with 28 general circulation models (GCMs) in Coupled Model Inter-comparison Project phase 5. Using the most appropriate site-specific CDFs, the spatial and temporal variations of the nine EPIs for the historical and projected future periods at 10-, 20-, 50- and 100-year return periods were investigated. The results showed that the GEV, Pearson-III, three- and two-parameter log-normal were generally the best CDFs for the 9 EPIs in China. By comparing the results during 2021–2100 with 1961–2017, the return periods increased as the EPIs increased. It was especially apparent in southeast China where the annual mean precipitation was above 1300 mm. The increases of the trends were significant for EPIs (especially in northwestern China), including the maximum 1 day precipitation, number of heavy precipitation days, number of very heavy precipitation days, extremely wet days and annual total wet day precipitation. The simple daily intensity index increased in northeast China, decreased in western China, but had no significant change in other regions. The maximum 5-day precipitation and consecutive wet days decreased in most areas except western China. The consecutive dry days decreased in northern China and increased in southeast China. This study provides region- and site-specific optimal CDFs and return period information and reveals the spatiotemporal changes of 9 EPIs at different return periods of 10-, 20-, 50- and 100-years under the RCP 4.5 and RCP 8.5 scenarios for 2021–2100. The obtained results are useful for guiding disaster-prevention efforts in different regions of China.

118‐year climate and extreme weather events of Metropolitan Manila in the Philippines

AbstractMetropolitan Manila, the Philippines, is a megacity with a population of 12.9 million people. Unabated urbanization and disorganized infrastructure build‐up, coupled with a large urban poor population have made many of its population vulnerable to climate change. This study presents the 118‐year urban climate and extreme weather events of Metropolitan Manila. Daily average and minimum temperature are on the rise comparable to countrywide trends. Consequently, there are more warm and less cold nights. Total annual precipitation is also increasing at a rate of 77.99 mm/decade. Decreasing simple daily intensity index implies that higher observed precipitation is due to the increase in wet days count rather than intensity. Tropical cyclones (TCs) are critical in producing most extreme rainfall events in the metropolis. Extreme precipitation is induced either by a TC's immediate rainbands or remote precipitation effects by enhancing the prevailing summer monsoon flow. TC‐induced rain modulates annual rainfall variability and is estimated to contribute 45.2% to Metropolitan Manila mean total rainfall.

Spatial and temporal rainfall changes in Egypt.

During the twentieth century, the intensity and frequency of extreme events (e.g., storms and floods) have significantly altered globally due to human-induced climate change. Recently, it has been recognized that some regions in Egypt have exposed to extreme rainfall events which led in some cases to severe flash floods. In this work, the variability of rainfall characteristics in Egypt was investigated based on a detailed statistical analysis of historical rainfall records at 31 stations. Both parametric (Pearson) and non-parametric (Mann-Kendall and Spearman) tests were applied on annual and seasonal precipitation indices to examine temporal trends. A classification of significant trends was introduced to assess the degrees of their likelihood. The results detected significant trends in annual indices: maximum precipitation, total precipitation, simple daily intensity index, and number of rainy days at 29, 19, 19, and 13% of stations, respectively. Significant trends in seasonal indices were also found at a few stations. For all indices, 77% of the detected significant trends are negative concluding a decrease in the amount of precipitation in Egypt. Additionally, only 6% of the detected trends are classified as less likely, while the rest is likely and extremely likely, indicating a high probability of most detected trends. Generally, the detected trends do not form any spatial pattern in all cases. The results also provided a preliminary impression on the likely impacts of climate change on rainfall characteristics in Egypt.

Long-term trends in precipitation indices at eastern districts of Bangladesh

This study analyzed the trends of extreme daily rainfall indices over three meteorological stations located in the eastern region of Bangladesh from 1960 to 2000. The climate change-related indices included frequency-based indices: number of heavy rainfall days and consecutive dry and wet days, and intensity-based indices: annual wet-day rainfall total, daily and consecutive five-day maximum rainfall, very and extremely wet days and simple daily intensity index. The magnitude of trends in extreme rainfall indices time series was determined using the nonparametric Sen’s slope estimator method, and the statistical significance of the trends was analyzed using the Mann–Kendall test. The rainfall trends exhibited regional patterns. Overall, results suggested an increase in annual rainfall over the study area; however, a tendency toward reduction of rainfall in the wet season was observed. Analysis of extreme rainfall indices demonstrated non-significant increase in frequency of heavy rainfall days, decrease in consecutive dry days and increase in consecutive wet days coupled with regional decline in daily and consecutive five-day maximum rainfall in the monsoon.

Historical extreme rainfall events in southeastern Australia

The cities of Melbourne, Sydney and Adelaide are home to almost half of the Australian population, and are often exposed to extreme rainfall events and high year-to-year rainfall variability. However the majority of studies into rainfall in these cities, and southeastern Australia in general, are limited to the 20th century due to data availability. In this study we use rainfall data from a range of sources to examine four rainfall indices for Melbourne, Sydney and Adelaide for 1839–2017. We derive the total rainfall, number of raindays, wettest day of the month and the simple daily intensity index for each city over the past 178 years, and find relatively consistent relationships between all indices despite potential data quality issues associated with the historical data. We identify several extreme daily rainfall events in the pre-1900 period in Sydney and Melbourne that warrant further examination as they appear to be more extreme than anything in the modern record. We find a moderate and relatively stable relationship between El Niño–Southern Oscillation (ENSO) and annual variations of total rainfall and the number of raindays at all three cities over the research period, but no relationship between ENSO and the annual wettest day, in agreement with other studies using shorter time series.

Observed changes in precipitation totals in Poland

This paper examines observed changes in the indices of mean precipitation in Poland, based on daily precipitation records for 45 stations in Poland from 1961 to 2017. Changes in annual, semi-annual, seasonal, as well as monthly precipitation totals are examined. In addition, changes in the number of days with precipitation (≥ 1 mm), as well as in the Simple Daily Intensity Index and the ratio of precipitation in the warm half-year to precipitation in the cold half-year are studied. Many changes are detected, but most of them are not statistically significant at the 0.1 level. Yet, there are regionally consistent seasonal changes, with a dominating clear precipitation increase in spring and winter. The Student’s t-test for the comparison of means for two intervals: 1961–1990 and 1991–2017 revealed statistically significant increases for annual and spring precipitation, as well as for Simple Daily Intensity Index, and monthly data: increases for February, March, July, September, October and decreases for: June, August, November, December.

Analysis of Precipitation Extremes in the Source Region of the Yangtze River during 1960–2016

The source region of the Yangtze River (SRYR) on the central Tibetan Plateau has seen one of the most significant increases in temperature in the world. Climate warming has altered the temporal and spatial characteristics of precipitation in the SRYR. In this study, we analyzed the temporal trends and spatial distributions of extreme precipitation in the SRYR during 1960–2016 using 11 extreme precipitation indices (EPIs) derived from daily precipitation data collected at five meteorological stations in the region. The trends in the EPIs were estimated using the linear least squares method, and their statistical significance was assessed using the Mann–Kendall test. The results show the following. Temporally, the majority of SRYR EPIs (including the simple daily intensity index, annual maximum 1-day precipitation (RX1day), annual maximum 5-day precipitation (RX5day), very wet day precipitation, extremely wet day precipitation, number of heavy precipitation days, number of very heavy precipitation days, and number of consecutive wet days) exhibited statistically nonsignificant increasing trends during the study period, while annual total wet-day precipitation (PRCPTOT) and the number of wet days exhibited statistically significant increasing trends. In addition, the number of consecutive dry days (CDD) exhibited a statistically significant decreasing trend. For the seasonal EPIs, the PRCPTOT, RX1day, and RX5day all exhibited nonsignificant increasing trends during the wet season, and significant increasing trends during the dry season. Spatially, changes in the annual and wet season EPIs in the study area both exhibited significant differences in their spatial distribution. By contrast, changes in dry season PRCPTOT, RX1day, and RX5day exhibited notable spatial consistency. These three indices exhibited increasing trends at each station. Moreover, there was a statistically significant positive correlation between the annual PRCPTOT and each of the other EPIs (except CDD). However, the contribution of extreme precipitation to annual PRCPTOT exhibited a nonsignificant decreasing trend.

Extreme temperature and rainfall events in National Capital Region of India (New Delhi) in the recent decades and its possible impacts

Intergovernmental Panel on Climate Change (IPCC) promulgated a clear message that there have been many extreme weather and climate events observed globally since 1950, and these changes occurred mainly due to anthropogenic causes and emission of greenhouse gases. A computation study was carried out to assess the extreme temperature and rainfall events for the period 1984–2015 at the Indian Agricultural Research Institute, New Delhi by using ETCCDI indices through RClimDex software. The statistical significance of time series data and various calculated indices was done by linear regression as well as by Mann-Kendall test. Results indicated that annual mean maximum temperature decreased significantly at 0.019 °C/year and annual mean minimum temperature showed an increasing trend but without statistical significance. Alteration has happened in atmospheric properties, both physical and chemical over Delhi region during the period because of rapid urbanization and, increased concentration of aerosol. Fossil fuel/biomass waste burning, transportation of sand dust from Thar Desert, and reduction in incoming solar radiation have contributed both for fall in daytime temperature and rise in nighttime temperature. The changes in temperature would affect agricultural production through reduction in the rate of photosynthesis and excessive nocturnal respiration. Frequency and magnitude of coolest day (maximum temperature < 15 °C) and night (minimum temperature < 5 °C) have been rising at IARI, New Delhi. In the case of rainfall-based indices, annual rainfall (PRCPTOT), consecutive wet days (CWD), and number of days with rainfall ≥ 20 mm (R20) showed significant increasing tendency. Increasing trend in simple daily intensity index (SDII), rainy days (R2.5), and declining trend of consecutive dry days (CDD) indicates better distribution of rainfall. Nevertheless, increasing tendency in RX1day, RX5day, and R99p indicates possibilities of heavy rainfall events although the trend has been found insignificant.

Assessment of climate change for extreme precipitation indices: A case study from the central United States

Five extreme precipitation indicators were calculated on an annual basis for 1890 through 2013 and analysed to determine spatial patterns and temporal trends in the frequency and magnitude of observed extreme precipitation events in Kansas located in the central United States. Indicators were selected from the list of the World Meteorological Organization–Commission for Climatology (WMO–CCL) and the Research Programme on Climate Variability and Predictability (CLIVAR). The indicators included the number of days with precipitation greater than or equal to 10 mm/day (R10), maximum number of consecutive dry days (CDD; days with precipitation lower that 1 mm), maximum 5‐day precipitation total (R5D), and simple daily intensity index (SDII) which is the annual precipitation total divided by number of days with precipitation greater than or equal to 1 mm, and the fraction of annual total precipitation due to events exceeding the 95th percentile (R95T) based on the period 1961–1990. Positive trends in the results were found for a majority of stations for R10, R5D, SDII, and R95T. Consecutive dry days was the only index that had a negative trend at a majority of stations. Spatial pattern analysis indicates greater changes in frequencies and magnitudes for eastern Kansas. Results from this study highlight observed climate shifts in precipitation patterns with a tendency towards greater and more frequent extreme precipitation in eastern Kansas and a tendency towards drier conditions in western Kansas. These hydroclimatic adjustments can produce costly impacts in areas that include flood management, hydraulic structures, water availability throughout the year, agricultural production, ecosystems, and human health.

Changes in the temperature and precipitation extremes in China during 1961–2015

Based on daily maximum temperature (Tmax), daily minimum temperature (Tmin) and daily precipitation collected from 1867 meteorological stations in China from 1961 to 2015, the spatiotemporal variations in temperature and precipitation extremes and their associations with large-scale atmospheric and oceanic circulation patterns were analyzed using linear trend analysis, Pearson correlation analysis and Mann-Kendall method. Results indicate that both the maximum Tmin (TNx) and the minimum Tmin (TNn) had increased significantly at rates of 0–0.5 °C and 0.2–1.0 °C per decade respectively in most of China, whereas the trends in the maximum Tmax (TXx) and the minimum Tmax (TXn) were not significant, resulting in a decrease of diurnal temperature range (DTR) at rates of 0–0.7 °C per decade in most of northeastern China, northern China and western China. The percentage changes in TXn and TNn were much higher than those of TXx and TNx. For precipitation indices, simple daily intensity index (SDII) and extremely wet-day precipitation (R99p) had increased at rates of 0.10 mm/day and 2.6 mm per decade respectively, but the trends of maximum 1-day precipitation (Rx1day), maximum 5-day precipitation (Rx5day) and total wet-day precipitation (PRCPTOT) were not significant in China. The spatial trends of five precipitation indices were also not significant in almost the whole of China. Higher percentage changes of precipitation indices were mainly appeared in western China. Most of climatic indices had positive correlation with Atlantic multidecadal oscillation (AMO) and negative correlation with East Atlantic/Western Russia (EA/WR). The variations of TXx and TNx were more related to the variability of AMO and EA/WR in China, and those of TXn and TNn were more associated with the Arctic oscillation (AO) in northeastern China, northern China and northern Xinjiang. The variations of precipitation indices were not significantly related to the circulation patterns in the vast majority of China.

Trends in extreme rainfall over ecologically sensitive Western Ghats and coastal regions of Karnataka: an observational assessment

Rainfall is one of the pivotal climatic variables, which influence spatio-temporal patterns of water availability. In this study, we have attempted to understand the interannual long-term trend analysis of the daily rainfall events of ≥ 2.5 mm and rainfall events of extreme threshold, over the Western Ghats and coastal region of Karnataka. High spatial resolution (0.25° × 0.25°) daily gridded rainfall data set of Indian Meteorological Department was used for this study. Thirty-eight grid points in the study area was selected to analyze the daily precipitation for 113 years (1901–2013). Grid points were divided into two zones: low land (exposed to the sea and low elevated area/coastal region) and high land (interior from the sea and high elevated area/Western Ghats). The indices were selected from the list of climate change indices recommended by ETCCDI and are based on annual rainfall total (RR), yearly 1-day maximum rainfall, consecutive wet days (≥ 2.5 mm), Simple Daily Intensity Index (SDII), annual frequency of very heavy rainfall (≥ 100 mm), frequency of very heavy rainfall (≥ 65–100 mm), moderate rainfall (≥ 2.5–65 mm), frequency of medium rainfall (≥ 40–65 mm), and frequency of low rainfall (≥ 20–40 mm). Mann-Kendall test was applied to the nine rainfall indices, and Theil-Sen estimator perceived the nature and the magnitude of slope in rainfall indices. The results show contrasting trends in the extreme rainfall indices in low land and high land regions. The changes in daily rainfall events in the low land region primarily indicate statistically significant positive trends in the annual total rainfall, yearly 1-day maximum rainfall, SDII, frequency of very heavy rainfall, and heavy rainfall as well as medium rainfall events. Furthermore, the overall annual rainfall strongly correlated with all the rainfall indices in both regions, especially with indices that represent heavy rainfall events which is responsible for the total increase of rainfall.

Future changes in Asian summer monsoon precipitation extremes as inferred from 20-km AGCM simulations

This study examines the impacts of climate change on precipitation extremes in the Asian monsoon region during boreal summer, based on simulations from the 20-km Meteorological Research Institute atmospheric general circulation model. The model can capture the summertime monsoon rainfall, with characteristics similar to those from Tropical Rainfall Measuring Mission and Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation. By comparing the 2075–2099 with the present-day climate simulations, there is a robust increase of the mean rainfall in many locations due to a warmer climate. Over southeastern China, the Baiu rainband, Bay of Bengal and central India, extreme precipitation rates are also enhanced in the future, which can be inferred from increases of the 95th percentile of daily precipitation, the maximum accumulated precipitation in 5 consecutive days, the simple daily precipitation intensity index, and the scale parameter of the fitted gamma distribution. In these regions, with the exception of the Baiu rainband, most of these metrics give a fractional change of extreme rainfall per degree increase of the lower-tropospheric temperature of ~ 5 to 8.5% K−1, roughly consistent with the Clausius–Clapeyron relation. However, over the Baiu area extreme precipitation change scales as ~ 3.5% K−1 only. We have also stratified the rainfall data into those associated with tropical cyclones (TC) and those with other weather systems. The AGCM gives an increase of the accumulated TC rainfall over southeastern China, and a decrease in southern Japan in the future climate. The latter can be attributed to suppressed TC occurrence in southern Japan, whereas increased accumulated rainfall over southeastern China is due to more intense TC rain rate under global warming. Overall, non-TC weather systems are the main contributor to enhanced precipitation extremes in various locations. In the future, TC activities over southeastern China tend to further exacerbate the precipitation extremes, whereas those in the Baiu region lead to weaker changes of these extremes.

Precipitation Extremes in Dynamically Downscaled Climate Scenarios over the Greater Horn of Africa

This study first assesses the performance of regional climate models in the Coordinated Regional Climate Downscaling Experiment (CORDEX) in reproducing observed extreme precipitation indices over the Greater Horn of Africa (GHA) region during 1989–2005. The study then assesses projected changes in these extremes during 2069–2098 compared to 1976–2005. The Regional Climate Model (RCM) simulations are made using two RCMs, with large-scale forcing from four CMIP5 Global limate Models(GCMs) under two Representative Concentration Pathways (RCP4.5 and RCP8.5). We found that RCM simulations have reasonably captured observed patterns of moderate precipitation extreme indices (MPEI). Pattern correlation coefficients between simulated and observed MPEI exceed 0.5 for all except the Simple Daily Intensity Index (SDII). However, significant overestimations or underestimations exist over localized areas in the region. Projected changes in Total annual Precipitation (PRCPTOT) and the annual number of heavy (&gt;10 mm) and very heavy (&gt;20 mm) precipitation days by 2069–2098 show a general north-south pattern, with decreases over the southern half and increases over the northern half of the GHA. These changes are often greatest over parts of Somalia, Eritrea, the Ethiopian highlands and southern Tanzania. Maximum one- and five-day precipitation totals over a year and SDII (ratio of PRCPTOT to rainy days) are projected to increase over a majority of the GHA, including areas where PRCPTOT is projected to decrease, suggesting fewer, but heavier rainy days in the future. Changes in the annual sum of daily precipitation above the 95th and 99th percentiles are statistically significant over a few locations, with the largest projected decrease/increase over Eritrea and northwestern Sudan/Somalia. Projected changes in Consecutive Dry Days (CDD) suggest longer periods of dryness over the majority of the GHA, except the central portions covering northern Uganda, southern South Sudan, southeastern Ethiopia and Somalia. Substantial increases in CDD are located over southern Tanzania and the Ethiopian highlands. The magnitude and the spatial extent of statistically-significant changes in all MPEI increase from RCP4.5 to RCP8.5, and the separation between positive and negative changes becomes clearer under RCP8.5.