Wet Extremes Research Articles

An evaluation of the CORDEX regional climate models in simulating future rainfall and extreme events over Mzingwane catchment, Zimbabwe

The study evaluated CORDEX RCMs’ ability to project future rainfall and extreme events in the Mzingwane catchment using an ensemble average of three RCMs (RCA4, REMO2009 and CRCM5). Model validation employed the statistical mean and Pearson correlation, while trends in projected rainfall and number of rainy days were computed using the Mann-Kendall trend test and the magnitudes of trends were determined by Sen’s slope estimator. Temporal and spatial distribution of future extreme dryness and wetness was established by using the Standard Precipitation Index (SPI). The results show that RCMs adequately represented annual and inter-annual rainfall variability and the ensemble average outperformed individual models. Trend results for the projected rainfall suggest a significant decreasing trend in future rainfall (2016–2100) for all stations at p < 0.05. In addition, a general decreasing trend in the number of rainy days is projected for future climate, although the significance and magnitude varied with station location. Model results suggest an increased occurrence of future extreme events, particularly towards the end of the century. The findings are important for developing proactive sustainable strategies for future climate change adaption and mitigation.

Increasing impacts from extreme precipitation on population over China with global warming

Precipitation-related extremes are among the most impact-relevant consequences of a warmer climate, particularly for China, a region vulnerable to global warming and with a large population. Understanding the impacts and risks induced by future extreme precipitation changes is critical for mitigation and adaptation planning. Here, extreme precipitation changes under different levels of global warming and their associated impacts on populations in China are investigated using multimodel climate projections from the Coupled Model Intercomparison Project Phase 5 and population projections under Shared Socio-economic Pathways. Heavy precipitation would intensify with warming across China at a rate of 6.52% (5.22%–8.57%) per degree of global warming. The longest dry spell length would increase (decrease) south (north) of ~34°N. The low warming target of the Paris Agreement could substantially reduce the extreme precipitation related impacts compared to higher warming levels. For the area weighted average changes, the intensification in wet extremes could be reduced by 3.22%, 9.42% and 16.70% over China, and the lengthening of dry spells could be reduced by 0.72%, 4.75% and 5.31% in southeastern China, respectively, if global warming is limited to 1.5 °C as compared to 2, 3 and 4 °C. The Southeastern China is the hotspot of enhanced impacts due to the dense population. The impacts on populations induced by extreme precipitation changes are dominated by climate change, while future population redistribution plays a minor role.

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.

Tree rings reveal dry conditions during Charlemagne’s Fossa Carolina construction in 793 CE

The first navigable canal across the main European watershed in southern Germany was the most ambitious and visionary hydro-engineering project of the Early Middle Ages, known as Charlemagne’s Fossa Carolina. Hydrological conditions would have been crucial for both the construction process and subsequent navigability. Written sources specify that heavy rain was a crucial factor for the abandonment of the project in late 793 CE, a few months after digging began. Our understanding of past climate variability in this region is, however, limited by the lack of high-resolution proxy archives. Here, we use annually resolved and absolutely dated ring-width measurements of 2469 drought sensitive oaks (Quercus sp.) from Bavaria, Germany, to reconstruct regional changes in hydroclimate back to 500 CE. Periods of anomalously dry summers occurred from ∼600 to 800, ∼900–1000, ∼1200–1400 and ∼1700–1900 CE, whereas increased humidity characterized the 9th century, High Middle Ages (11th–12th century) and the 17th century CE. Relatively dry conditions during the construction period favoured the building progress of the Fossa Carolina. However, the heavy rain which stopped the project in 793 CE is not reflected in radial oak growth. This is likely related to i) the historically recorded event happened outside the growing season and ii) compared to dry extremes, wet extremes are generally less pronounced in tree-ring width. Nevertheless, our results provide the first local hydroclimate reconstruction covering the entire Early Middle Ages and thus, placing the Fossa Carolina in a long-term high-resolution environmental perspective.

DROUGHT ASSESSMENT OF IRAN USING THE MDI INDEX

Abstract. Drought is one of the most common natural phenomena. Many indices using multiple data types have been created, and their success at recognizing periods of extreme wetness and dryness has been well documented. The merit of the method is the utilization of terrestrial water storage (TWS) variations from Gravity Recovery and Climate Experiment (GRACE) quantification of drought intensity. Alongside with these observations, we add precipitation data to equations. In this study, we analyze Merged-dataset Drought index (MDI) using GRACE-derived TWSA and precipitation in Iran, where most of the area is desert and mountain in the middle and South of the country. Our sample period is from January 2003 to December 2014. MDI shows a strong correlation with existing drought indices, especially with the Palmer Drought Severity Index (PDSI). Based on the obtained results, MDI indicates a moderate Drought event in 2008 and 2012–2015, which is compatible with the recorded result of PDSI. The longest drought took 22 months (from January 2008 to October 2009). Interestingly, the coefficient of correlation between MDI and PDSI is 0.67.

Projecting Wet Season Rainfall Extremes Using Regional Climate Models Ensemble and the Advanced Delta Change Model: Impact on the Streamflow Peaks in Mkurumudzi Catchment, Kenya

Each year, many African countries experience natural hazards such as floods and, because of their low adaptative capabilities, they hardly have the means to face the consequences, and therefore suffer huge economic losses. Extreme rainfall plays a key role in the occurrence of these hazards. Therefore, climate projection studies should focus more on extremes in order to provide a wider range of future scenarios of extremes which can aid policy decision making in African societies. Some researchers have attempted to analyze climate extremes through indices reflecting extremes in climate variables such as rainfall. However, it is difficult to assess impacts on streamflow based on these indices alone, as most hydrological models require daily data as inputs. Others have analyzed climate projections through general circulation models (GCMs) but have found their resolution too coarse for regional studies. Dynamic downscaling using regional climate models (RCMs) seem to address the limitation of GCMs, although RCMs might still lack accuracy due to the fact that they also contain biases that need to be eliminated. Given these limitations, the current study combined both dynamic and statistical downscaling methods to correct biases and improve the reproduction of high extremes by the models. This study’s aim was to analyze extreme high flows under the projection of extreme wet rainfall for the horizon of 2041 of a Kenyan South Coast catchment. The advanced delta change (ADC) method was applied on observed data (1982–2005), control (1982–2005) and near future (2018–2041) from an ensemble mean of multiple regional climate models (RCMs). The created future daily rainfall time series was introduced in the HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modeling System) hydrological model and the generated future flow were compared to the baseline flow at the gaging station 3KD06, where the observed flow was available. The findings suggested that in the study area, the RCMs, bias corrected by the ADC method, projected an increase in rainfall wet extremes in the first rainy season of the year MAMJ (March–April–May–June) and a decrease in the second rainy season OND (October–November–December). The changes in rainfall extremes, induced a similar change pattern in streamflow extremes at the gaging station 3KD06, meaning that an increase/decrease in rainfall extremes generated an increase/decrease in the streamflow extremes. Due to lack of long-term good quality data, the researchers decided to perform a frequency analysis for up to a 50 year return period in order to assess the changes induced by the ADC method. After getting a longer data series, further analysis could be done to forecast the maximum flow to up to 1000 years, which could serve as design flow for different infrastructure.

Dynamical delimitation of the Central American Dry Corridor (CADC) using drought indices and aridity values

The Central American Dry Corridor (CADC) is a sub-region in the isthmus that is relatively drier than the rest of the territory. Traditional delineations of the CADC’s boundaries start at the Pacific coast of southern Mexico, stretching south through Central America’s Pacific coast down to northwestern Costa Rica (Guanacaste province). Using drought indices (Standardized Precipitation Index, Modified Rainfall Anomaly Index, Palmer Drought Severity Index, Palmer Hydrological Drought Index, Palmer Drought Z-Index and the Reconnaissance Drought Index) along with a definition of aridity as the ratio of potential evapotranspiration (representing demand of water from the atmosphere) over precipitation (representing the supply of water), we proposed a CADC delineation that changes for normal, dry and wet years. The identification of areas that change their classification during extremely dry conditions is important because these areas may indicate the location of future expansion of aridity associated with climate change. In the same way, the delineation of the CADC during wet extremes allows the identification of locations that remain part of the CADC even during the wettest years and that may require special attention from the authorities.

Multi-climate mode interactions drive hydrological and vegetation responses to hydroclimatic extremes in Australia

Australia has experienced a large frequency of hydroclimatic events since the early 21st century, with multiple large-scale droughts and flooding rains exerting dramatic impacts on water resources and ecosystems. Despite these pronounced consequences, the coupling of ecosystem functioning to extreme climate variability remains elusive due to the lack of complete understanding of hydrological connections. In this study, we investigated the spatiotemporal trends of Australia's hydrological and vegetation responses to three climate modes: El Niño-Southern Oscillation, the Indian Ocean dipole and the Southern Annular Mode, utilizing climate indices, satellite-derived total water storage anomaly (TWSA) from GRACE, precipitation from TRMM and vegetation greenness from MODIS. Using partial cross-correlation and vegetation sensitivity analyses to interpret the interactions among climate modes, water resources and vegetation across Australia, three hydroclimatic extreme events from 2002 to 2017 were analyzed: (i) a prolonged drought (2002–09, colloquially known as the ‘big dry’); (ii) a dramatic wet pulse (2010–11, the ‘big wet’); and (iii) another anomalous El Niño event (2015).Our results showed the entire continent partitioned into three geographic zones with diverse drying and wetting trends in total water storage, precipitation and vegetation greenness, reflecting varying and fundamental influences from the individual climate modes. Ecosystem productivity was found to be better related and more sensitive to TWSA than precipitation across different hydroclimate zones and during both extreme dry and wet conditions. We also observed TWSA increased rapidly during wet extremes, and these gains in water resources persisted for an additional four years (i.e., TWSA remained positive until 2015 following the 2011 ‘big wet’). Lastly, findings from another hydroclimatic event (the 2015 El Niño drought) further confirmed the relationships among climate, water and ecosystems, demonstrating the feasibility of predicting ecohydrological implications of future hydroclimatic extremes in Australia.

Experimental warming amplified opposite impacts of drought vs. wet extremes on ecosystem carbon cycle in a tallgrass prairie

Climate warming is leading to greater precipitation variability, resulting in increased frequency and intensity of both drought and wet extremes. However, how these extreme events interact with climate warming and hay-harvest in grasslands to impact ecosystem functions has not yet been well explored. In this study, we took advantage of a long-term experiment to examine how climate warming and clipping (i.e., mimicking hay harvest) regulated impacts of naturally occurring drought and wet extremes on ecosystem CO2 fluxes of a tallgrass prairie in the Great Plains, USA. Warming resulted in net ecosystem carbon release (i.e., positive net ecosystem CO2 exchange, NEE) in the extreme drought year of 2011, but significantly enhanced net carbon uptake in the extremely wet year of 2015 in comparison with NEE in normal years. Warming-induced carbon release in the drought year was due to significantly enhanced ecosystem respiration (ER) from mid-summer to early-autumn, whereas warming-enhanced NEE in the wet year was due to an increase in aboveground net primary production (ANPP) compared to those in normal years. Drought diminished warming-induced increases in ANPP to about one sixth of that in the wet year in the unclipped plots. Interestingly, clipping offset the drought-mediated ecosystem carbon loss by increasing GPP and weakened the wet-enhanced ANPP. Overall, our results suggest that a future, warmer climate may exacerbate carbon losses in terrestrial ecosystems during drought extremes but stimulate the ecosystem carbon sink under wet extremes.

A Modified Framework for Quantifying Land–Atmosphere Covariability during Hydrometeorological and Soil Wetness Extremes in Oklahoma

AbstractGlobal “hot spots” for land–atmosphere coupling have been identified through various modeling studies—both local and global in scope. One hot spot that is common to many of these analyses is the U.S. southern Great Plains (SGP). In this study, we perform a mesoscale analysis, enabled by the Oklahoma Mesonet, that bridges the spatial and temporal gaps between preceding local and global analyses of coupling. We focus primarily on east–west variations in seasonal coupling in the context of interannual variability over the period spanning 2000–15. Using North American Regional Reanalysis (NARR)-derived standardized anomalies of convective triggering potential (CTP) and the low-level humidity index (HI), we investigate changes in the covariance of soil moisture and the atmospheric low-level thermodynamic profile during seasonal hydrometeorological extremes. Daily CTP and HI z scores, dependent upon climatology at individual NARR grid points, were computed and compared to in situ soil moisture observations at the nearest mesonet station to provide nearly collocated annual composites over dry and wet soils. Extreme dry and wet year CTP and HI z-score distributions are shown to deviate significantly from climatology and therefore may constitute atmospheric precursors to extreme events. The most extreme rainfall years differ from climatology but also from one another, indicating variability in the strength of land–atmosphere coupling during these years. Overall, the covariance between soil moisture and CTP/HI is much greater during drought years, and coupling appears more consistent. For example, propagation of drought during 2011 occurred under antecedent CTP and HI conditions that were identified by this study as being conducive to positive dry feedbacks demonstrating potential utility of this framework in forecasting regional drought propagation.

Debris flows in southeast Australia linked to drought, wildfire, and the El Niño–Southern Oscillation

Between 2003 and 2013, drought, large wildfires, and record-breaking rainfall contributed to debris flows in southeast Australia that appear to be unprecedented in spatial extent and density in historical records. Here, we used a debris-flow inventory from this period of dry and wet extremes to examine the processes and climatic controls underlying the regionwide debris-flow response. Results reveal shallow landslides and surface runoff as two distinct initiation mechanisms, linked to different geologic settings and contrasting hydroclimatic conditions. Landslide-generated debris flows occurred in sandy soils, independent of past fires, and were tightly controlled by extreme rainfall causing saturation and mass failure during La Nina periods. In contrast, runoff-generated debris flows occurred in clay-rich soils from short and intense rainstorms after wildfires in dry conditions, often associated with El Nino. Thus, it appears that both ends of the wet and dry climate extremes produce the same general geomorphic response, debris flows, but in different areas and by different initiation processes. Debris-flow activity is therefore at a maximum when amplitude and frequency of climate oscillations are large. Debris flows in southeast Australia are likely to become more frequent and widespread as wildfire activity and rainfall intensity are predicted to increase.

Inter-comparison of remotely sensed precipitation datasets over Kenya during 1998–2016

The paucity of reliable ground based datasets remains a major challenge over Kenya. In the advent of extreme wetness or drought events, reliable precipitation estimates for local characterization is a long overdue process. In the present study, four Satellite derived Precipitation Estimates (SPE): TMPA V7 3B42, PERSIANN-CDR, CHIRPS, and ARC2, are assessed over four homogeneous zones in Kenya with gauge based data during 1998–2016. Results show that variations of SPE products are based on complex geomorphology of different climatic zones. All SPE products depict bimodal annual precipitation pattern with west-east gradient representing heavier to lighter precipitation events. The Monthly analysis reveal good statistical agreement with reference datasets despite underestimation of precipitation in most regions. Seasonal precipitation events show that the PERSIANN-CDR perform better along low altitude humid climate and western zones around Lake Basin while ARC2 has uniform performance as gauge stations over highlands regions. Strong positive linear relationship on annual scale is evident in most SPE products with CHIRPS, ARC2, and TMPA exhibiting relatively high correlation (r) and minimum root mean square error (RMSE), except for PERSIANN-CDR. Overall, the findings of this study show the potentials of SPE products for applications over study domain. The TMPA V7 and PERSIANN-CDR could be useful in understanding individual floods events. Since the CHIRPS perform relatively well over ASAL regions, it could be utilized in monitoring droughts events.

Climate Factors Leading to Asymmetric Extreme Capture in the Tree‐Ring Record

AbstractPaleoclimate data play a critical role in contextualizing recent hydroclimate extremes, but asymmetries in tree‐ring responses to extreme climate conditions pose challenges for reconstruction and interpretation of past climate. Here we establish the extent to which existing tree‐ring records capture precipitation extremes in western North America and evaluate climate factors hypothesized to lead to asymmetric extreme capture, including timing of precipitation, seasonal temperatures, snowpack, and atmospheric river events. We find that while there is dry‐biased asymmetry in one third of western North American tree‐ring records, 45% of sites capture wet extremes as well as or better than dry extremes. Summer extremes are rarely captured at any sites. Latitude and elevation affect site‐level extreme responses, as do seasonal climate conditions, particularly in the autumn and spring. Directly addressing asymmetric extreme value capture in tree‐ring records can aid our interpretation of past climate and help identify alternative avenues for future reconstructions.

Tendency towards a more extreme precipitation climate in the Coupled Model Intercomparison Project Phase 5 models

Extremity of precipitation climate can be evaluated by the intensity of both wet and dry extremes. Here we illustrate the tendency towards more extreme precipitation climate during the 21st century in a multi‐model ensemble of 32 climate model simulations from the Coupled Model Intercomparison Project Phase 5. We compare the projected changes in two climatic indices describing the extremity of precipitation climate. One index, the maximum 1‐d precipitation (R1d) represents the wet and another, the maximum number of consecutive dry days (CDD), represents the dry extremes. Averaged over the globe, both indices are projected to increase, implying an overall tendency towards more extreme precipitation climate. The projected increase, in relative terms, is approximately twice as large in R1d as in CDD. Also on a regional scale, in almost all global land areas the precipitation climate is rather projected to become more than less extreme. Two thirds of these areas exhibit a more pronounced change in wet than dry extremes and slightly less than one third of the areas showing a more pronounced change in dry than wet extremes. Only over limited areas the precipitation climate shows a tendency towards less extreme conditions. In reproducing the observed mean precipitation in 1971–2000, the models tend to be too wet in dry regions and too dry in wet regions. There are not any consistent differences in the tendency towards more extreme precipitation climate among the models depending on their horizontal or vertical resolution.

Jet stream dynamics, hydroclimate, and fire in California from 1600 CE to present

Moisture delivery in California is largely regulated by the strength and position of the North Pacific jet stream (NPJ), winter high-altitude winds that influence regional hydroclimate and forest fire during the following warm season. We use climate model simulations and paleoclimate data to reconstruct winter NPJ characteristics back to 1571 CE to identify the influence of NPJ behavior on moisture and forest fire extremes in California before and during the more recent period of fire suppression. Maximum zonal NPJ velocity is lower and northward shifted and has a larger latitudinal spread during presuppression dry and high-fire extremes. Conversely, maximum zonal NPJ is higher and southward shifted, with narrower latitudinal spread during wet and low-fire extremes. These NPJ, precipitation, and fire associations hold across pre-20th-century socioecological fire regimes, including Native American burning, postcontact disruption and native population decline, and intensification of forest use during the later 19th century. Precipitation extremes and NPJ behavior remain linked in the 20th and 21st centuries, but fire extremes become uncoupled due to fire suppression after 1900. Simulated future conditions in California include more wet-season moisture as rain (and less as snow), a longer fire season, and higher temperatures, leading to drier fire-season conditions independent of 21st-century precipitation changes. Assuming continuation of current fire management practices, thermodynamic warming is expected to override the dynamical influence of the NPJ on climate-fire relationships controlling fire extremes in California. Recent widespread fires in California in association with wet extremes may be early evidence of this change.

The response of precipitation characteristics to global warming from climate projections

Abstract. We revisit the issue of the response of precipitation characteristics to global warming based on analyses of global and regional climate model projections for the 21st century. The prevailing response we identify can be summarized as follows: increase in the intensity of precipitation events and extremes, with the occurrence of events of “unprecedented” magnitude, i.e., a magnitude not found in the present-day climate; decrease in the number of light precipitation events and in wet spell lengths; and increase in the number of dry days and dry spell lengths. This response, which is mostly consistent across the models we analyzed, is tied to the difference between precipitation intensity responding to increases in local humidity conditions and circulations, especially for heavy and extreme events, and mean precipitation responding to slower increases in global evaporation. These changes in hydroclimatic characteristics have multiple and important impacts on the Earth's hydrologic cycle and on a variety of sectors. As examples we investigate effects on potential stress due to increases in dry and wet extremes, changes in precipitation interannual variability, and changes in the potential predictability of precipitation events. We also stress how the understanding of the hydroclimatic response to global warming can provide important insights into the fundamental behavior of precipitation processes, most noticeably tropical convection.

Enhanced growth after extreme wetness compensates for post-drought carbon loss in dry forests

While many studies have reported that drought events have substantial negative legacy effects on forest growth, it remains unclear whether wetness events conversely have positive growth legacy effects. Here, we report pervasive and substantial growth enhancement after extreme wetness by examining tree radial growth at 1929 forest sites, satellite-derived vegetation greenness, and land surface model simulations. Enhanced growth after extreme wetness lasts for 1 to 5 years and compensates for 93 ± 8% of the growth deficit after extreme drought across global water-limited regions. Remarkable wetness-enhanced growths are observed in dry forests and gymnosperms, whereas the enhanced growths after extreme wetness are much smaller in wet forests and angiosperms. Limited or no enhanced growths are simulated by the land surface models after extreme wetness. These findings provide new evidence for improving climate-vegetation models to include the legacy effects of both drought and wet climate extremes.

Characterizing and Monitoring Drought over Upper Blue Nile of Ethiopia with the Aid of Copula Analysis

The main aim of this study is to characterize and monitor drought distribution and expansion over Upper Blue Nile of Ethiopia by using univariate standard precipitation index (SPI) and standardized soil moisture index (SMI) whose joint distribution leads to multi standardized drought index (MSDI). The soil moisture and CHIRPS precipitation data from first January 1980 to 2016 are modeled. The indices of SPI, SMI and the joint MSDI value over the Upper Blue Nile are analyzed. The SPI for different time scales is implemented. The correlation between severity, duration and intensity including wetness and drought strengths is computed and analyzed. It is found that the correlation between duration and severity is 0.96 and normal conditions for SPI 3, 6, 12 month time scales are frequently observed rather than moderate, severe and extreme severe drought or wetness. Building on soil moisture and precipitation data of the summer season, the Clayton copula model is selected based on goodness of fit parameters. After setting the best copula family for the Upper Blue Nile then we applied the joint distribution method is applied for characterizing and monitoring drought. It is found that the MSDI more clearly showed that the severity of drought across the time series of each time scales, than SPI and SMI. As the time scale increases there is decline of fluctuation or frequency of drought and the rising of drought duration is shown by SPI, SMI and MSDI. By using SPI6, SMI6 and MSDI6 the spatial distribution of drought is determined from June to August in the years 1984 and 2015 indicate the drought expansions in the eastern and western parts of Upper Blue Nile during the respective years.

The Relationship between Wave Trains in the Southern Hemisphere Storm Track and Rainfall Extremes over Tasmania

Abstract We assess the large-scale atmospheric dynamics influencing rainfall extremes in Tasmania, located within the Southern Hemisphere storm track. We characterize wet and dry multiday rainfall extremes in western and eastern Tasmania, two distinct climate regimes, and construct atmospheric flow composites around these extreme events. We consider the onset and decay of the events and find a link between Rossby wave trains propagating in the polar jet waveguide and wet and dry extremes across Tasmania. Of note is that the wave trains exhibit varying behavior during the different extremes. In the onset phase of rainfall extremes in western Tasmania, there is a coherent wave train in the Indian Ocean, which becomes circumglobal in extent and quasi-stationary as the event establishes and persists. Wet and dry extremes in this region are influenced by opposite phases of this circumglobal wave train pattern. In eastern Tasmania, wet extremes relate to a propagating wave train, which is first established in the Indian Ocean sector and propagates eastward to the Pacific Ocean sector as the event progresses. During dry extremes in eastern Tasmania, the wave train is first established in the Pacific Ocean, as opposed to Indian Ocean, and persists in this sector for the entire event, with a structure indicative of the Pacific–South American pattern. The findings regarding different wave train forms and their relationship to rainfall extremes have implications for extreme event attribution in other regions around the globe.

Carbon exchange responses of a mesic grassland to an extreme gradient of precipitation.

Growing evidence indicates that ecosystem processes may be differentially sensitive to dry versus wet years, and that current understanding of how precipitation affects ecosystem processes may not be predictive of responses to extremes. In an experiment within a mesic grassland, we addressed this uncertainty by assessing responses of two key carbon exchange processes-aboveground net primary production (ANPP) and soil respiration (Rs)-to an extensive gradient of growing season precipitation. This gradient comprised 11 levels that specifically included extreme values in precipitation; defined as the 1st, 5th, 95th, and 99th percentiles of the 112-year climate record. Across treatments, our experimental precipitation gradient linearly increased soil moisture availability in the rooting zone (upper 20cm). Relative to ANPP under nominal precipitation amounts (defined as between the 15th and 85th percentiles), the magnitude of ANPP responses were greatest to extreme increases in precipitation, with an underlying linear response to both precipitation and soil moisture gradients. By contrast, Rs exhibited marginally greater responses to dry versus wet extremes, with a saturating relationship best explaining responses of Rs to both precipitation and soil moisture. Our findings indicate a linear relationship between ANPP and precipitation after incorporating responses to precipitation extremes in the ANPP-precipitation relationship, yet in contrast saturating responses of Rs. As a result, current linear ANPP-precipitation relationships (up to ~ 1000mm) within mesic grasslands appear to hold as appropriate benchmarks for ecosystems models, yet such models should incorporate nonlinearities in responses of Rs amid increased frequencies and magnitudes of precipitation extremes.