Changes In Rainfall Amounts Research Articles

Orbital modulation of subtropical versus subantarctic moisture sources in the southeast Pacific mid-latitudes

Reconstructing rainfall variability and moisture sources is a critical aspect to understand past and future hydroclimate dynamics. Here, we use changes in the deuterium content of land-plant leaf waxes from two marine sediment cores located off Chile to reconstruct changes in rainfall amount and variation in moisture sources over the last ~50 ka. The records indicate increased moisture in central Chile during precession maxima, but an obliquity modulation is evident in southern Chile. While the southern westerly winds are the dominant factor of precipitation in southern Chile by bringing moisture and perturbations from the extratropics, the subtropics represent an additional moisture source during precession maxima due to a stronger subtropical jet increasing moisture transport from the tropics to the mid-latitudes. These findings imply that a combination of orbital modulation of moisture sources and rainfall amount explains the last glacial moisture maximum and early Holocene moisture minimum in south-central Chile.

Correlation between flood couplet-based sediment yield and rainfall patterns in a small watershed on the Chinese Loess Plateau

Understanding how rainfall patterns impact sediment yields during rainfall events is important to explore soil erosion changes and to prevent watershed flood disasters. However, few studies identified sediment yields variation affected by rainfall patterns at continuous deposited flood couplet scale. This study analyzed sediment yields under different rainfall patterns and correlated particle depositional features on the condition that the erosive environment was obviously changed by anthropogenic activities in a check dam-controlled small watershed on the Chinese Loess Plateau. Results showed that erosive rainfall events, having formed 40 flood couplets behind the check dam between 1978 and 2010, can be grouped into three rainfall patterns (i.e., rainfall patterns I, II, and III) according to changes in rainfall amount, erosivity, and duration. Rainfall pattern III, characterized by high rainfall amount and erosivity within a short duration (i.e., rainstorm) accounted for only 15.0 % of erosive rainfall events while yielding 44.7 % of the total sediment. Conversely, rainfall pattern I (the most common, 55.0 %), characterized by its long duration and relatively low rainfall amount and erosivity, only contributed 25.3 % of the total sediment. Both sediment yields and thickness proportions of coarse particle layer in flood couplets exhibited a decreasing trend under all three rainfall patterns. Meanwhile, the main factor that impacted sediment yields changed from rainfall in the 1980s and 1990s to the “Grain for Green” program dominated anthropogenic activities since 1999. For a small watershed with a few terraces and only one check dam at the outlet, artificial vegetation restoration significantly reduced coarse soil particle loss and sediment yield. Findings showed that sediment yield and deposition feature variations in flood couplets under different rainfall patterns are helpful in improving watershed soil and water conservation measures against flood disasters, particularly under rainstorms.

Projected changes in rainfall amount and distribution in the Democratic Republic of Congo – Evidence from an ensemble of high-resolution climate simulations

Extreme precipitation has been threatening many sectors of human society and is likely to intensify with global warming. In the present study, we have analysed the impact of future climate change on daily mean rainfall and heavy rainfall on seasonal and annual scales in the Democratic Republic of Congo (DRC) by using ten long-term runs of high-resolution regional climate models. We initially assessed the performance of each run and the multi-model ensemble mean in simulating the daily mean rainfall (PRE), the maximum one-day rainfall (Rx1day), the simple rainfall intensity index (SDII), the count of days when rainfall is greater than or equal to 20 mm (RR20mm), the total rainfall when the daily rainfall exceeds the 95th percentile of the wet-day rainfall (R95p) and the maximum number of consecutive days with more than or equal to 1 mm (CWD). Next, we examined the future changes of these indices, focusing on the multi-model ensemble mean and spread under the high emission scenario RCP8.5. The time frames considered are the mid and end of the twenty-first century (2035–2065 and 2070–2100, respectively). The results indicate that the performance of REMO2015-MPI-ESM was close to the multi-model ensemble mean in representing the mean rainfall and most heavy rainfall indices, while CanRCM4-CamESM2 was identified as the worst performing model. The key finding of this study is that the multi-model ensemble mean project no significant change regarding the daily mean rainfall throughout the year and across all seasons by the middle of the 21st century, except of the western region of the country where a decrease is projected. Simultaneously, Rx1day, SDII, RR20mm, and R95p are projected to decrease almost everywhere during all seasons. Moreover, a consistent decrease in the number of wet days is projected. Focusing on the end of the century, the multi-model ensemble mean project an overall decrease in daily mean rainfall, especially in the western region of the DRC, with a more pronounced effect during MAM. The increase in Rx1day, SDII, RR20mm, and R95p, along with a decrease in CWD, is amplified in this period. These findings are useful for predicting the potential threats of precipitation-related diseases and natural hazards, as well as for designing climate-resilient infrastructure and socioeconomic activities in the DRC.

Effects of moderate drought extension on bacterial network structure in the rhizosphere soil of Leymus chinensis in semi-arid grasslands.

Grasslands are home to complex bacterial communities whose dynamic interactions play a crucial role in organic matter and nutrient cycling. However, there is limited understanding regarding the impact of changes in rainfall amount and the duration of dry intervals on bacterial interactions. To assess the impact of changes in precipitation volume and dry intervals on bacterial co-occurrence networks, we carried out precipitation manipulation experiments in the Eastern Eurasian Steppe of China. We found that alterations in precipitation and dry intervals did not significantly affect bacterial alpha and beta diversity. However, we observed significant changes in the co-occurrence network structure of bacteria in the rhizosphere ecosystem, with the 12-day dry interval showing the most notable reduction in the number of degrees, edges, and clustering coefficient. Additionally, the study identified putative keystone taxa and observed that the moderately prolonged dry intervals between precipitation events had a major effect on the robustness of bacterial networks. The complexity and stability of the network were found to be positively correlated, and were primarily influenced by soil water content, phosphorous, and aboveground biomass, followed by available phosphorus (AP) and total biomass. These findings have the potential to enhance our comprehension of how bacterial co-occurrence pattern react to variations in dry intervals, by regulating their interactions in water-limited ecosystems. This, in turn, could aid in predicting the impact of precipitation regime alterations on ecosystem nutrient cycling, as well as the feedback between ecosystem processes and global climate change.

Multi-proxy validation of glacial-interglacial rainfall variations in southwest Sulawesi

Speleothem δ18O is widely used as a proxy for rainfall amount in the tropics on glacial-interglacial to interannual scales. However, uncertainties in the interpretation of this renowned proxy pose a vexing problem in tropical paleoclimatology. Here, we present paired multi-proxy geochemical measurements for stalagmites from southwest Sulawesi, Indonesia, and confirm changes in rainfall amount across ice age terminations. Collectively, the stalagmites span two glacial-interglacial transitions from ~380,000 to 330,000 and 230,000 to 170,000 years ago. Mg/Ca in the slow-growing stalagmites is affected by water moving through the karst and prior calcite precipitation, making it a good proxy for changes in local rainfall. When paired, Mg/Ca and δ18O corroborate prominent shifts from drier glacials to wetter interglacials in the core of the Australasian monsoon domain. These shifts in rainfall occur 4,000-7,000 years later than glacial-interglacial increases in global temperature and the associated response of Sulawesi vegetation, determined by speleothem δ13C.

Controls on Speleothem Initial 234U/238U Ratios in a Monsoon Climate

AbstractSpeleothem initial uranium isotope ratios ((234U/238U)i) can be influenced by processes along the seepage water flow‐path including alpha‐recoil into porewater during 238U decay and hostrock weathering, the balance of which can reflect the infiltration rate. Thus, speleothem (234U/238U)i may provide information about past changes in rainfall amounts. However, the utility of (234U/238U)i as a paleo‐infiltration proxy has only been explored in a limited set of rainfall regimes. We present a speleothem (234U/238U)i record from Mawmluh Cave in northeast India, an area influenced by the Indian Summer Monsoon, covering 1964–2012 CE. Speleothem (234U/238U)i was relatively constant from 1964 to 1984 but then linearly increased by 0.05 over ∼15 years, a trend that does not correspond with observed rainfall changes. To evaluate potential drivers of (234U/238U)i variability, we model the evolution of water (234U/238U) in a simple karst system using an advection‐reaction model parameterized by Mawmluh Cave variables. Although varying infiltration influences modeled water (234U/238U), the larger, sustained change observed in the speleothem record can only be modeled by varying the U concentration and (234U/238U) of the weathering hostrock. This suggests that larger shifts in speleothem (234U/238U)i may result from flow path changes, bringing waters in contact with hostrock of variable U characteristics. Consideration of published Mawmluh Cave records suggests that these mechanisms may also explain variability in stalagmite (234U/238U)i on precessional timescales. Further examination of speleothems (234U/238U)i from climates characterized by high rainfall and extensive weathering is warranted to better constrain the controls on (234U/238U)i in these dynamic environments.

Changes in rainfall amount and seasonality modulate taxonomic, functional, and phylogenetic diversity in a gypsophilous plant community in the Chihuahuan Desert

ABSTRACT Background Climate change is expected to alter future rainfall regime in arid zones, which may impact gypsophilous plant diversity components in the Chihuahuan Desert. Aims We investigated the effects of different rainfall timings and amounts on the taxonomic, functional, and phylogenetic components of a gypsophilous plant community. Methods We used soil monoliths extracted from the southern Chihuahuan Desert in a greenhouse experiment with three rainfall timings (typical, early, and late) and two rainfall amounts (100% and 50%) and evaluated the effects on taxonomic, functional, and phylogenetic diversity. Results Irrigation treatment with 50% of average rainfall reduced species richness and plant abundance and altered species composition. At 100% irrigation, specific leaf area was lower in the treatments with typical and late rainfall timing than in the treatment with early rainfall. Phylogenetic diversity was significantly lower in the late timing treatment in November. Conclusion Our study evidence that the water shortage impacted drastically on the plant community by decreased species richness and diversity. Nevertheless, late rainfall can buffer the effects of water diminution but only on taxonomic and functional diversity, with the opposite effect on the phylogenetic diversity, in the gypsophilous communities in the Chihuahuan Desert.

Response of biocrust nitrogenase activity to the variation of rainfall regime in the Tengger Desert, northern China

In arid desert regions, a large proportion of the ground surface is covered by specialized organisms such as cyanobacteria and mosses that form biological soil crusts (BSCs), which have multifunctionality in the ecosystem via stabilizing soil and fixing nitrogen (N) and carbon (C). Climate change, especially variations in rainfall will alter BSC species composition, cover and biomass, shaping the N-fixation of BSCs. Although BSCs are main contributors of N in desert ecosystems, it is not clear how nitrogenase activity (NA) of BSCs responds to changes in rainfall amount and frequency to function in the N-cycle. To address this important knowledge gap, based on long-term rainfall monitoring and predicted scenarios, we designed five levels of rainfall amount ranging from decreased by 50% to increased by 50%, and five rainfall frequencies ranging from increased by 100% to decreased by 80%, to simulate the potential variation of rainfall using rainout shelters. The NA of bare soil and cyanobacteria- and moss-dominated crust soil (three soil types) was determined by acetylene reduction assay. The soil water content (SWC), oxidable C and microbial biomass C and N were also determined. The NA of the three soil types was positively correlated with their SWC when rainfall amount decreased. In the case of increased rainfall frequency, NA of bare soil and moss-dominated crust was positively correlated with SWC, but negatively correlated for cyanobacteria-dominated crust. However, with increased rainfall amount combined with decreased rainfall frequency, there was no significant relationship between NA and SWC. In addition, NA of BSC was higher than that of bare soil with increased rainfall amount combined with decreased rainfall frequency, while that of bare soil was higher than that of BSC for decreased rainfall amount combined with increased rainfall frequency. In the case of increased frequency combined with decreased rainfall amount, the NA was higher for moss-dominated than cyanobacteria-dominated crust, but higher for cyanobacteria-dominated than moss-dominated crust for reduced rainfall frequency combined with increased rainfall amount. Meanwhile, NA of both bare soil and moss-dominated crust was correlated with microbial biomass C; and NA of cyanobacteria-dominated crust was positively correlated with SWC as well as oxidable C. Our findings indicated that future changes in rainfall regime will strongly affect NA of BSCs and bare soil in arid desert regions, and consequently change the soil fertility and net primary production.

Variability and Changes in Rainfall Observed Across Jharkhand Region (India)

Abstract: Rainfall variability has a substantial impact on water supplies, agricultural output, and, as a result, the economy. It examines the historical spatiotemporal variability and trend of rainfall on Jharkhand's annual and seasonal time series state over a 60-year period (1954–2013). The goal of this study was to find trends in long and short-term changes in rainfall amounts in the Jharkhand region at various spatial scales. With the help of the wavelet technique, we were able to determine the periodicity of rainfall over time and identify active and break days in the monsoon season. When the OLR positive anomaly increases, rainfall decreases (Break days), and when the OLR negative anomaly increases, rainfall increases (Active days). The Indian summer monsoon extreme is also strongly linked to the Equatorial Indian Ocean Oscillation (EQUINOO), which is based on surface zonal wind across the central equatorial Indian Ocean. Because the Bay of Bengal is next to Jharkhand, local disturbances or cyclonic events are also discovered and their impact on rainfall is investigated. Keywords: Rainfall, ENSO, Wavelet Transform, Active and Break days, Cyclone, Climate Change.

Tree growth responses to temporal variation in rainfall differ across a continental-scale climatic gradient.

Globally, many biomes are being impacted by significant shifts in total annual rainfall as well as increasing variability of rainfall within and among years. Such changes can have potentially large impacts on plant productivity and growth, but remain largely unknown, particularly for much of the Southern Hemisphere. We investigate how growth of the widespread conifer, Callitris columellaris varied with inter-annual variation in the amount, intensity and frequency of rainfall events over the last century and between semi-arid (<500 mm mean annual rainfall) and tropical (>800 mm mean annual rainfall) biomes in Australia. We used linear and polynomial regression models to investigate the strength and shape of the relationships between growth (ring width) and rainfall. At semi-arid sites, growth was strongly and linearly related to rainfall amount, regardless of differences in the seasonality and intensity of rainfall. The linear shape of the relationship indicates that predicted future declines in mean rainfall will have proportional negative impacts on long-term tree growth in semi-arid biomes. In contrast, growth in the tropics showed a weak and asymmetrical (‘concave-down’) response to rainfall amount, where growth was less responsive to changes in rainfall amount at the higher end of the rainfall range (>1250 mm annual rainfall) than at the lower end (<1000 mm annual rainfall). The asymmetric relationship indicates that long-term growth rates of Callitris in the tropics are more sensitive to increased inter-annual variability of rainfall than to changes in the mean amount of rainfall. Our findings are consistent with observations that the responses of vegetation to changes in the mean or variability of rainfall differ between mesic and semi-arid biomes. These results highlight how contrasting growth responses of a widespread species across a hydroclimatic gradient can inform understanding of potential sensitivity of different biomes to climatic variability and change.

Responses of CH4 flux and microbial diversity to changes in rainfall amount and frequencies in a wet meadow in the Tibetan Plateau

Global climate change scenarios forecast an increasing occurrence frequency of extreme precipitation events in the Qinghai-Tibet Plateau, events that likely will result in increasing amounts of annual rainfall. Increased precipitation and changes in its frequency may influence CH4 production. However, few studies have reported the responses of CH4 flux and soil microbes to increases in the amount and frequency of precipitation in alpine wet meadows. In this study, we experimentally altered the amount and frequency of precipitation events during the plant growing season (May to September) in 2019 at a wet meadow in the Qinghai-Tibet Plateau. All treatments included ambient rain (CK) plus 25 mm of extra water for each irrigation event but with different irrigation frequency (i.e., weekly (DF1), biweekly (DF2), every three weeks (DF3) and every four weeks (DF4)). Compared with CK (rainfall is 600 mm from May to September), the increase in rainfall frequency and amount not only affected the bacterial community structure and relative abundances of dominant genera in the soil, but also increased aboveground biomass and soil water-filled pore space (WFPS), and ultimately promotes CH4 emission. We also found that CH4 flux was positively correlated with soil temperature, easily-oxidizable organic carbon, particulate organic carbon, WFPS and ammonium nitrogen. In contrast, CH4 flux was negatively correlated with bulk density, microbial biomass carbon and dissolved organic carbon contents. Furthermore, among biological factors, vegetation biomass indirectly affected CH4 emissions by affecting the substrate supply of methanogens and the transport capacity of CH4 flux. Redundancy analysis showed that the CH4 flux was positively correlated with Acidobacteria, and negatively correlated with Proteobacteria. This study suggests that changes in rainfall amount and frequency in the future will lead to the increase in CH4 flux and will impact wet meadow carbon-sink function by affecting soil microbial abundance and community structure.

Observed changes in rainfall amount and extreme events in southeastern Ethiopia, 1955–2015

This study analysed spatio-temporal variability and trends in rainfall amount and extreme events in the southeastern part of Ethiopia for the period 1955–2015. Daily rainfall data from 44 recording stations were used to define total rainfall amounts and 12 extreme event indices for three wet seasons and annual time scale. Mann–Kendall’s trend test and Sen’s slope estimator were used to determine trends and rates of change, respectively. Results showed the emergence of different trend signals across seasons and over space in the study area. Trend tests for total rainfall amount and extreme indices for annual and March–May season show a global significant downward tendency. However, the number of wet and dry days, maximum consecutive wet and dry spells and wet day rainfall intensity for the annual time scale show mixed significant upward and downward tendencies, while trends for the number of dry days and maximum consecutive dry spells showed a global significant increasing trend for the March–May season across the study area. On the other hand, mixed global significant upward and downward tendencies were found in all rainfall indices for the June–September season over the northern part of the study area. Different from the two wet seasons, the trend test for the September–November wet season in the southern part of the study area shows an increasing tendency, although only few of the upward trends were statistically significant. In contrast, the number of dry days and maximum dry spell length for this season reveal decreasing trends at most of the stations. Empirical evidences generated in rainfall trends using dense gauging stations provide useful information to develop spatially relevant climate change adaptation and climate risk management plans.

Climate and land-use effects on hydrological and vegetation signals during the last three millennia: Evidence from sedimentary leaf waxes in southwestern Morocco

The southwest of Morocco is considered to be an area of refuge within the Mediterranean region, hosting the endemic tropical Argan tree. This region is presently subject to severe droughts, desertification and land degradation, and likely facing increased climate variability and socio-economic stress in the future. Here, we use the stable hydrogen and carbon isotope composition (δD and δ13C) of plant-waxes in a high-resolution marine sediment core (GeoB8601-3) collected off Cape Ghir in southwestern Morocco, in combination with published data on pollen and XRF element ratios from the same archive. We aim to reconstruct the hydroclimate and vegetation history during the last 3000 years. Stable carbon isotope compositions of leaf waxes (δ13Cwax) show that natural vegetation in southwestern Morocco consists of C3 plants. Minor variations in δ13Cwax were positively correlated to changes in stable hydrogen isotope compositions of leaf waxes (δDwax) before 700 CE. Changes in rainfall amounts and water use efficiency indicate a clear vegetation response to precipitation changes and thus to climate forcing. After 700 CE, δDwax and δ13Cwax became de-coupled suggesting that the plant wax discharge and their isotope signals were no longer solely controlled by climate; the waxes likely mainly originate from the lowlands and carry an enriched (dry) δD signal but a depleted 13C signature. The depletion of δ13Cwax correlates with the increase of Argan pollen concentration in the record. The period between ~700 and 900 CE coincides with the Arabization of Morocco which had an impact on the demographic composition of the country leading to new agricultural habits and, as a result, on the land-use triggering a higher erosion of lowland material by the Souss River.

Deforestation Impacts on Orographic Precipitation in the Tropical Andes

This study examines the implications of Tropical Montane Forests (TMFs) loss on orographic precipitation in the Eastern slopes of the Andes (EADS). The focus is on moist processes for synoptic regimes associated with significant EADS precipitation: (1) monsoon rainfall for weak and strong South America Low-Level Jet (LLJ) conditions and (2) heavy rainfall associated with cold air intrusions (CAI) in the dry season. High-resolution simulations using the Weather Research and Forecasting (WRF) model were conducted for realistic and modified land-cover resulting from the conversion of TMFs to savanna. The deforestation scenarios result in 50–100% decrease (up to ∼400 J kg–1) in Convective Available Potential Energy (CAPE) spatially organized by land-cover change along the EADS. Analysis of the differences in simulated frequency distributions of rainfall intensity shows robust daytime increases in light rainfall (&amp;lt;2 mm h–1) and decreases in moderate rainfall rates (2–10 mm h–1) in the altitudinal band 500–2,000 m where orographic enhancement is dominant. Whereas there are negligible changes in the spatial patterns of precipitation and hydrologic response for monsoon conditions, rainfall accumulations decrease for all cases, and the precipitation maxima shift downslope into the Amazon lowlands. Changes in rainfall amount and intensity result in runoff decreases of 5–10% at the event-scale for the CAI case. Sensitivity simulations for lower initial soil moisture conditions indicate a strong positive feedback of forest loss to hydrologic drought along the EADS foothills in the austral spring when CAIs play a key role in the tropical EADS dry season hydrometeorology.

Speleothem record from Pentadactylos cave (Cyprus): new insights into climatic variations during MIS 6 and MIS 5 in the Eastern Mediterranean

A new paleoclimate record from Cyprus gives valuable insights into climatic variations during Marine Isotope Stages (MIS) 6–5 for the East Mediterranean region. Two stalagmites from Pentadactylos cave in the Kyrenia mountain range (800 m altitude) in Cyprus grew from 174.6 ± 0.7 to 112.2 ± 0.5 ka BP with major hiatuses at 163–142 and 132–128 ka. During early MIS6 the stalagmite suggests through a relatively low growth rate (57–5 mm/ka) and variable, but rather negative d18O that climate conditions were highly variable on a millennial scale, with wet and cold climate conditions during Sapropel 6 deposition. At the end of MIS6 (141–132 ka), growth rate varied from 123 to 18 mm/ka and less negative δ 18 O c suggests general dry/cold conditions followed by a growth stop during H11. The onset of MIS5e is marked by the highest growth rate (217 mm/ka). The most negative δ18O values at the onset and during the Eemian wet period in Cyprus are driven mostly by the source effect (Sapropel 5) and enhanced rainfall amounts. Stable conditions during MIS 5e were rather short as shown in the growth and isotopic signal, consistent with other EM records. After 122 ka, growth decreased drastically (8–2 mm/ka) and a slow deterioration of the soil cover is suggested from continuously less negative δ13C values. Fluid inclusion d18O shows a clear shift (4–5‰) between end-MIS 6 and MIS 5e. Clumped isotopes measurements indicate kinetic effects between calcite and water of up to ∼1‰. After correction for kinetic effects using Δ47, a minimum estimate for the MIS 6–5 temperature shift in the EM is ca. 9 °C. Similarly, drastic changes in rainfall amounts are inferred from measured (fluid inclusion) and calculated water d18O.

Extreme drought alters progeny dispersal unit properties of winter wild oat (Avena sterilis L.).

The dead husk is a vital component of the dispersal unit whose biochemical properties can be modified following exposure to drought. This might affect seed performance and fate, soil properties and consequently plant biodiversity. We investigated the effects of extreme drought on the dispersal unit (DU) properties of winter wild oat (Avena sterilis L.) in the Mediterranean ecosystems focusing on a commonly ignored component of the DU, namely the dead floral bracts (husk). DUs were collected from a climate change experimental research station in the Judean Hills, Israel, simulating extreme drought and from two additional sites differing in the rainfall amounts. Our results showed that drought conditions significantly affected A. sterilis reproductive traits displaying reduced DUs and caryopses weights. The husk contributes profoundly to seed performance showing that germination from the intact DUs or the intact florets 1 was higher, faster and more homogenous compared to naked caryopses; no effect of drought on germination properties was observed. The husk stored hundreds of proteins that retain enzymatic activity and multiple metabolites including phytohormones. Changes in rainfall amounts affected the composition and levels of proteins and other metabolites accumulated in the husk, with a notable effect on abscisic acid (ABA). The husk of both control and drought plants released upon hydration substances that selectively inhibited other species seed germination as well as substances that promoted microbial growth. Our data showed that the dead husk represents a functional component of the DU that have been evolved to nurture the embryo and to ensure its success in its unique habitat. Furthermore, drought conditions can modify husk biochemical properties, which in turn might affect seed performance and fate, soil microbiota and soil fertility and consequently plant species diversity.

Hydroclimate variability of western Thailand during the last 1400 years

Mainland Southeast Asia is located on the moisture transport route of the Indian summer monsoon (ISM) where hydroclimate records from speleothems have rarely been investigated. Here, we present a new multi-proxy (δ18O and δ13C values, trace element concentrations, and grayscale values) data set of stalagmite KPC1 from Khao Prae cave in western Thailand spanning the last 1400 years (500–1900 CE; the Common Era). These multi-proxy data reveal a high variability between the wet and dry periods during 500–850 CE and 1150–1300 CE, stable climate conditions during 850–1150 CE, and overall dry conditions since 1300 CE. The δ13C values, trace elements concentrations, and grayscale values show centennial-scale fluctuations, which were probably driven by local hydrological processes. In contrast, variations in the stalagmite δ18O values reflect integrated changes in rainfall amount from the ISM. The KPC1 record agrees with other speleothem δ18O records of Southeast Asian summer monsoon from the last millennium, as well as the lake multi-proxy and tree-ring PDSI data from Mainland Southeast Asia, but diverges from records from the Indo-Pacific equatorial regions and the western Pacific. We conclude that hydroclimate variability at the western side of Mainland Southeast Asia is mainly driven by changes in moisture transport of the ISM. On socially relevant timescales, the KPC1 data set shows that a period of stable rainfall (850–1150 CE) coincides with the early success of the early empires (e.g., Pagan, Angkor, and Dai Viet) in Mainland Southeast Asia. In line with previous studies in the region, we speculate that the high variability in rainfall between 1150 and 1300 CE and droughts during 1300–1550 CE played a significant role in the demise of ancient societies in Southeast Asia.

Climate-smart agriculture, household income and asset accumulation among smallholder farmers in the Nyando basin of Kenya

Climate change, characterized by rising average temperatures and changes in rainfall amounts and patterns, remains a major threat to rural livelihoods. For smallholder households that heavily depend on agriculture, adaptation and mitigation measures, including coping strategies are therefore needed to secure household livelihoods and incomes. In this article, we assess the impacts on livelihood outcomes, of climate smart agricultural (CSA) practices that are promoted as adaptative strategies against effects of climate change. Using data from a survey of households in Nyando basin in Kenya, we combine statistical matching and simultaneous equation econometric modelling, to evaluate pathways through which CSA practices impact on household asset accumulation and income. We find that uptake of multiple stress-tolerant crops improves household income by 83%, which in turn improves household asset accumulation. Impact pathway modelling also show that adoption of improved livestock breeds significantly reduces household income by 76%. For improved livestock, however, household income does not impact on asset accumulation, possibly because income is invested in form of livestock rather than household assets. These findings show that adoption of multiple stress-tolerant crops improves household assets accumulation via the income pathway. However, given an option, households would invest increased incomes in livestock assets, confirming that livestock are a form of savings, which can be liquidated to bridge household income gaps. This is a better resilience measure as compared to investment in domestic household assets.

RAINFALL CHANGE DETECTION IN AFRICA USING REMOTE SENSING AND GIS BETWEEN 1999 – 2018

Many researchers used gauge data from weather stations for rainfall estimate across Africa. Since Africa lies within the tropics, there is possibility for variations in rain received from place to place. Therefore, there is need for excessive density of the gauges for accurate estimate of Africa’s rainfall. Due to numerous challenges, these cannot be achieved. This necessitates the application of remote sensing and GIS to detect changes in rainfall amount in Africa between 1999 and 2018. The data used was obtained from remote sensing satellite (TRMM) and analyzed using GIS application (IDRISI Taiga). The Simple Image Differencing was performed on the two annual mean images covering January to December, 1999 and January to December, 2018. This provides reliable information on rainfall estimate that can complement sparsely and unevenly distributed rain gauge network in Africa. The analysis shows that latitudinal locations, to some extent, determine spatial distribution of rainfall in Africa. It is also observed that significant changes in rainfall rate are mainly found around coastal regions. It was recommended that adequate ground data it needed to confirm these findings. African countries should provide adequate and justly distributed weather stations with on-net database for easy access to the data.

Rainfall manipulation experiments as simulated by terrestrial biosphere models: Where do we stand?

Changes in rainfall amounts and patterns have been observed and are expected to continue in the near future with potentially significant ecological and societal consequences. Modelling vegetation responses to changes in rainfall is thus crucial to project water and carbon cycles in the future. In this study, we present the results of a new model-data intercomparison project, where we tested the ability of 10 terrestrial biosphere models to reproduce the observed sensitivity of ecosystem productivity to rainfall changes at 10 sites across the globe, in nine of which, rainfall exclusion and/or irrigation experiments had been performed. The key results are as follows: (a) Inter-model variation is generally large and model agreement varies with timescales. In severely water-limited sites, models only agree on the interannual variability of evapotranspiration and to a smaller extent on gross primary productivity. In more mesic sites, model agreement for both water and carbon fluxes is typically higher on fine (daily-monthly) timescales and reduces on longer (seasonal-annual) scales. (b) Models on average overestimate the relationship between ecosystem productivity and mean rainfall amounts across sites (in space) and have a low capacity in reproducing the temporal (interannual) sensitivity of vegetation productivity to annual rainfall at a given site, even though observation uncertainty is comparable to inter-model variability. (c) Most models reproduced the sign of the observed patterns in productivity changes in rainfall manipulation experiments but had a low capacity in reproducing the observed magnitude of productivity changes. Models better reproduced the observed productivity responses due to rainfall exclusion than addition. (d) All models attribute ecosystem productivity changes to the intensity of vegetation stress and peak leaf area, whereas the impact of the change in growing season length is negligible. The relative contribution of the peak leaf area and vegetation stress intensity was highly variable among models.