Intra-annual Precipitation Variability Research Articles

Precipitation variation: a key factor regulating plant diversity in semi-arid livestock grazing lands.

Livestock presence impacts plant biodiversity (species richness) in grassland ecosystems, yet extent and direction of grazing impacts on biodiversity vary greatly across inter-annual periods. In this study, an 8-year (2014-2021) grazing gradient experiment with sheep was conducted in a semi-arid grassland to investigate the impact of grazing under different precipitation variability on biodiversity. The results suggest no direct impact of grazing on species richness in semi-arid Stipa grassland. However, increased grazing indirectly enhanced species richness by elevating community dominance (increasing the sheltering effect of Stipa grass). Importantly, intensified grazing also regulates excessive community biomass resulting from increased inter-annual wetness (SPEI), amplifying the positive influence of annual humidity index on species richness. Lastly, we emphasize that, in water-constrained grassland ecosystems, intra-annual precipitation variability (PCI) was the most crucial factor driving species richness. Therefore, the water-heat synchrony during the growing season may alleviate physiological constraints on plants, significantly enhancing species richness as a result of multifactorial interactions. Our study provides strong evidence for how to regulate grazing intensity to increase biodiversity under future variable climate patterns. We suggest adapting grazing intensity according to local climate variability to achieve grassland biodiversity conservation.

Altered intra-annual precipitation patterns affect the N-limitation status of soil microorganisms in a semiarid alpine grassland

The ongoing intensification of the hydrological cycle due to global climate change alters intra-annual precipitation variability. Changes in precipitation patterns lead to disparities in soil moisture; however, the responses of soil extracellular enzyme activities (EEAs) and microbial metabolism limitations to them is unclear. This study conducted an in situ field experiment in the alpine grasslands of the Kunlun Mountains to simulate the same amount of precipitation but change the distribution time of precipitation within the plant growing season. We examined the effects of variability in intra-annual precipitation patterns on the stoichiometry of topsoil (0–5 and 5–20 cm) properties, microbial biomass, and EEAs. Results showed that altered precipitation patterns significantly increased soil moisture’s disparity index (D) by 57 %–89 %. The activity of nitrogen-acquiring enzymes (L-leucine aminopeptidase) was increased by 20.82–32.08 % (P < 0.05) with increased variability of precipitation, while phosphorus-acquiring enzymes (Acid phosphatase) and carbon-acquiring enzymes (β-glucosidase) both decrease by 9.25–23.35 % and by 17.86–33.04 %, respectively (P < 0.05). We determined that soil microorganisms in the study region were metabolism-limited by nitrogen (vector angles < 45◦), and increased precipitation variability exacerbated nitrogen limitation (decrescent vector angles) and alleviated carbon limitation (shortened vector length). In addition, soil EEAs can be both interactively influenced by biotic and abiotic factors, with abiotic factors (i.e., D, soil organic carbon content, and soil total nitrogen content) having a stronger effect. Our study provides an effective strategy for regulating soil EEAs, microbial biomass, and microbial metabolism limitation and contributes to developing nutrient management and restoration strategies in semiarid alpine grassland ecosystems.

Belowground growth strategies of native and invasive rhizomatous perennial grasses in response to precipitation variability, clipping, and competition

Invasive clonal species may exhibit different growth strategies than their native clonal competitors. In this study, we examined the spatial distribution of tiller outgrowth and the bud bank by comparing the investment in phalanx versus guerilla growth of a native and invasive perennial grass in North America. We also examined the effect of altered precipitation frequency, clipping, and competition on their clonal growth strategies. Investment in phalanx and guerilla growth was assessed by examining live propagule and tiller production from the plant crown versus its rhizomes. Although invasive Bromus inermis and native Pascopyrum smithii exhibited similar clonal growth strategies as young seedlings, their clonal growth strategies significantly differed by the end of their first growing season. Pascopyrum smithii invested in dual phalanx and guerilla tiller outgrowth and bud placement, and B. inermis primarily invested in phalanx tiller outgrowth and bud placement. Competition rather than intra-annual precipitation variability and clipping altered the clonal growth strategy of these species. Intra- and inter- specific competition did not alter tiller outgrowth for either species. However, inter-specific competition caused both species to alter their bud placement. Bromus inermis shifted more buds from phalanx to guerilla positions while P. smithii shifted in the opposite direction. This may enable invasive B. inermis to expand while confining native P. smithii to more localized areas in the future. Clonal growth strategies appear to be species specific and responsive to inter-specific competition. Investigating the belowground bud aspect of clonal growth can reveal the mechanism driving the future aboveground clonal growth strategy of native and invasive rhizomatous grasses and help inform the patterns of invasion within a plant community.

Global vegetation resilience linked to water availability and variability

Quantifying the resilience of vegetated ecosystems is key to constraining both present-day and future global impacts of anthropogenic climate change. Here we apply both empirical and theoretical resilience metrics to remotely-sensed vegetation data in order to examine the role of water availability and variability in controlling vegetation resilience at the global scale. We find a concise global relationship where vegetation resilience is greater in regions with higher water availability. We also reveal that resilience is lower in regions with more pronounced inter-annual precipitation variability, but find less concise relationships between vegetation resilience and intra-annual precipitation variability. Our results thus imply that the resilience of vegetation responds differently to water deficits at varying time scales. In view of projected increases in precipitation variability, our findings highlight the risk of ecosystem degradation under ongoing climate change.

Intra-annual growing season climate variability drives the community intra-annual stability of a temperate grassland by altering intra-annual species asynchrony and richness in Inner Mongolia, China.

Understanding the factors that regulate the functioning of our ecosystems in response to environmental changes can help to maintain the stable provisioning of ecosystem services to mankind. This is especially relevant given the increased variability of environmental conditions due to human activities. In particular, maintaining a stable production and plant biomass during the growing season (intra‐annual stability) despite pervasive and directional changes in temperature and precipitation through time can help to secure food supply to wild animals, livestock, and humans. Here, we conducted a 29‐year field observational study in a temperate grassland to explore how the intra‐annual stability of primary productivity is influenced by biotic and abiotic variables through time. We found that intra‐annual precipitation variability in the growing season indirectly influenced the community intra‐annual biomass stability by its negative effect on intra‐annual species asynchrony. While the intra‐annual temperature variability in the growing season indirectly altered community intra‐annual biomass stability through affecting the intra‐annual species richness. At the same time, although the intra‐annual biomass stability of the dominant species and the dominant functional group were insensitive to climate variability, they also promoted the stable community biomass to a certain extent. Our results indicate that ongoing intra‐annual climate variability affects community intra‐annual biomass stability in the temperate grassland, which has important theoretical significance for us to take active measures to deal with climate change.

Belowground mechanism reveals climate change impacts on invasive clonal plant establishment

Climate change and disturbance can alter invasion success of clonal plants by differentially affecting the clonal traits influencing their establishment as young plants. Clonal traits related to the vegetative reproduction of native Pascopyrum smithii and non-native Bromus inermis grass seedlings were evaluated under altered precipitation frequencies and a single grazing event. Pascopyrum smithii maintained similar vegetative reproduction under three simulated precipitation frequencies whereas B. inermis vegetative reproduction declined as precipitation became more intermittent. Vegetative reproduction of the non-native B. inermis was greater than the native P. smithii under all simulated precipitation frequencies except the most intermittent scenario. A single grazing event did not affect either species’ response to intra-annual precipitation variability but did slightly reduce their clonal growth and increase their bud dormancy. In young plants, clonal traits of the invasive grass favored its superior expansion and population growth compared to the native grass except under the most severe climate change scenario. Grassland restoration using native P. smithii seeds would be successful in most years due to its resilient clonal growth in a changing climate. Clonal infrastructure development in young plants is critical to clonal plant establishment and persistence in a changing climate and under disturbed conditions.

Long-term regional changes in inter-annual precipitation variability in the Campania Region, Southern Italy

Precipitation variability in space and time has been a focus of research over the past decades. The largest body of literature was essentially focused on long-term changes in average climates and in climate extremes. Analyses of the changes in the inter-annual climate variability (the year-to-year variability), which represent an index of climatic risk, received instead very less attention, but it represents an important issue in order to quantitatively measure the socioeconomic impact of climate change impact over water resources. In order to depict a general characterization of the long-term climate variability for the Campania region, located in Southern Italy within the Mediterranean basin, an analysis of the precipitation coefficient of variation, assumed as an index of inter-annual climate variability, was performed over the period 1918–2015 and compared with the annual precipitation regime and the intra-annual precipitation variability of the same region. The Mann–Kendall and the modified Mann–Kendall tests were applied to detect the sign and significance of the temporal changes and Sen’s test was applied to quantify the temporal changes in inter-annual variability. The results illustrated a generalized condition (73% of total stations) of statistically significant increase of inter-annual variability distributed almost over the whole analyzed area, even though the detected change appeared rather moderate in magnitude. The relationship between annual precipitation, intra-annual precipitation variability, and inter-annual precipitation variability was not clearly identified for the studied region, likely because of the characteristics of climatic homogeneity for the area under investigation. However, the comparative analyzes clearly showed how, if the variations in the annual precipitation regime and in the intra-annual precipitation variability are poorly significant (respectively for 9% and 11% of total station), changes in inter-annual precipitation variability are strongly marked over the studied region.

Ecosystem hydrologic and metabolic flashiness are shaped by plant community traits and precipitation

Understanding the hydrologic and carbon cycling consequences of precipitation variability in dryland ecosystems requires improved appreciation and accounting of how above- and belowground biophysical processes differ in their response to rainfall. Our objective was to contrast the sensitivity of dryland ecosystem evapotranspiration (ET), gross ecosystem productivity (GEP), and ecosystem respiration (Re) in response to inter- and intra-annual precipitation variability in a nearby grassland, savanna, and shrubland ecosystems in southeastern Arizona. To do this, we modified the Richards-Baker index, which quantifies the flashiness of a stream’s hydrograph, to calculate analogous indices of ecosystem hydrologic and metabolic flashiness. In this way, ecosystem flashiness describes the frequency and rapidity of short-term fluctuations in H2O and CO2 exchange in response to precipitation while preserving the sequence of day-to-day variation in fluxes using tower-based time-series of daily averaged ET, GEP and Re. We calculated annual hydrologic, GEP, and Re flashiness (fET, fGEP and fRe respectively) using 6 years of daily-averaged fluxes estimated from eddy covariance. In contrast to our prediction, annual fGEP was consistently greater than annual fRe. Furthermore, we predicted that increasing rooting depth would correlate with a decline in annual fET and fGEP. In fact, annual fGEP was similar between the grassland, savanna, and shrubland. Whereas the response of annual fET and fGEP to annual precipitation was plant community dependent and generally declined with increasing rainfall, annual fRe did not vary in response to precipitation. The effect of late summer storms on fGEP was plant community dependent such that shrubland fGEP and fRe strongly declined in response to rainfall whereas grassland and savanna fGEP was relatively unresponsive. Conceptually similar to hydrologic flashiness, ecosystem flashiness may provide an additional lens through which to observe the influence of resource availability, shifts in community composition, and disturbance on ecosystem hydrologic and carbon cycling.

Impact of climate change on precipitation patterns in Houston, Texas, USA

Abstract Extreme precipitation events damage infrastructure and property; thus, predicting future precipitation patterns in the context of climate change is important. In this study, precipitation projections from 36 downscaled General Circulation Models (GCMs) under two Representative Concentration Pathway (RCP) scenarios (RCP2.6 and RCP8.5) enabled examination of projected changes in future precipitation for the Clear Creek watershed in Houston, Texas, USA. Precipitation from 1950 to 2099 simulated with GCM were downscaled using the Bias-Correction Spatial Disaggregation method. Ten precipitation indices that represent precipitation amount, precipitation intensity, precipitation duration, and precipitation frequency evaluated how precipitation patterns will likely change. Results show that, at the annual scale, mean precipitation will significantly decrease based on RCP8.5, or remain relatively constant based on RCP2.6. Precipitation intensity and precipitation variability, however, will likely increase. Dry periods will lengthen significantly, whereas the length of wet spells will generally remain unchanged. At the monthly scale, the amount of precipitation, precipitation intensity, precipitation frequency and the length of wet spells will likely increase in September. In contrast, precipitation will likely decrease and dry spells will lengthen in April, May, August, November, and December. This finding illustrates that the intra-annual variability in precipitation will increase. The projected changes in precipitation under RCP8.5 are generally greater compared with RCP2.6. Differences between the scenarios are more pronounced towards the end of the century. Houston has recently experienced substantial precipitation variability, including severe drought and record-breaking precipitation from Hurricane Harvey in 2017. These events are consistent with the long-term GCM projections. Findings from this study can be applied to help manage water resources and enhance adaptability to climate change.

Spatial variability analysis of precipitation and its concentration in Chaharmahal and Bakhtiari province, Iran

The spatial variability of annual precipitation and precipitation concentration has been analyzed in Chaharmahal and Bakhtiari province using data from 42 stations between 1981 and 2012. For this purpose, the correlation decay distance (CDD) and the coefficient of variation of annual precipitation have been computed at each station to show the inter-annual variability of precipitation. Results showed an increasing gradient from the southwest to the northeast in inter-annual precipitation variability. The degree of seasonality of precipitation and the year-to-year precipitation concentration variability were also investigated using the precipitation concentration index (PCI) and the coefficient of variation of PCI, respectively. The spatial distributions of intra-annual precipitation variability (or precipitation concentration) and inter-annual precipitation concentration showed a decreasing gradient from the southeast to the northwest. The T-mode principal component analysis (PCA) in association with cluster analysis (CA) was used to delineate homogeneous precipitation sub-zones for simplifying the spatial structure of precipitation variability over the region during the considered period. Results suggest three distinct sub-regions, including the northeastern part (the driest sub-region with the highest precipitation variability), the central and southern parts (the sub-region with the highest degree of seasonality of precipitation), and the northwestern part (the rainiest sub-region with the lowest inter-annual and intra-annual precipitation variability).

Seasonal Effects of Extreme Weather Events on Potential Extracellular Enzyme Activities in a Temperate Grassland Soil

Magnitude and timing of precipitation events within the growing season might be decisive for alterations in potential extracellular enzyme activity (PEEA), with consequences for nutrient cycle and carbon storage in grassland ecosystems. Pattern of PEEA catalyzing major steps of the carbon cycle (β-glucosidase (β-gls), cellobiohydrolase (cel), glucuronidase (glr) and xylosidase (xyl)), soil respiration rates and extractable organic carbon were analyzed in response to increased intra-annual precipitation variability in a European, mesic temperate grassland. The field experiment was carried out in three subsequent years by simulating recurrent drought events combined with heavy rainfall either early or late in the growing season (spring or summer) by rainout shelters and irrigation systems. Our data indicated comparable effects of the drought settings independent from the timing of the drought. Both for the simulated spring- and summer drought a decrease of enzymatic activities was observed compared to the control plots, with s-gls activity after the summer drought being the only exception. However, response pattern towards rewetting differed depending on the seasonal timing of the drought being introduced. After spring drought, a fast recovery to control level was observed for PEEA of s-gls and xyl, whereas cel and glr activity remained constantly lower. Rewetting after summer drought induced an increase of all enzymatic activities to values even higher compared to the controls. Overall, our data indicate a high resilience of PEEA towards drought and rewetting events in grassland soils, which is modulated by the seasonal timing of the extreme weather events.

Seasonal Drought Forecasting for Latin America Using the ECMWF S4 Forecast System

Meaningful seasonal prediction of drought conditions is key information for end-users and water managers, particularly in Latin America where crop and livestock production are key for many regional economies. However, there are still not many studies of the feasibility of such a forecasts at continental level in the region. In this study, precipitation predictions from the European Centre for Medium Range Weather (ECMWF) seasonal forecast system S4 are combined with observed precipitation data to generate forecasts of the standardized precipitation index (SPI) for Latin America, and their skill is evaluated over the hindcast period 1981–2010. The value-added utility in using the ensemble S4 forecast to predict the SPI is identified by comparing the skill of its forecasts with a baseline skill based solely on their climatological characteristics. As expected, skill of the S4-generated SPI forecasts depends on the season, location, and the specific aggregation period considered (the 3- and 6-month SPI were evaluated). Added skill from the S4 for lead times equaling the SPI accumulation periods is primarily present in regions with high intra-annual precipitation variability, and is found mostly for the months at the end of the dry seasons for 3-month SPI, and half-yearly periods for 6-month SPI. The ECMWF forecast system behaves better than the climatology for clustered grid points in the North of South America, the Northeast of Argentina, Uruguay, southern Brazil and Mexico. The skillful regions are similar for the SPI3 and -6, but become reduced in extent for the severest SPI categories. Forecasting different magnitudes of meteorological drought intensity on a seasonal time scale still remains a challenge. However, the ECMWF S4 forecasting system does capture the occurrence of drought events for the aforementioned regions and seasons reasonably well. In the near term, the largest advances in the prediction of meteorological drought for Latin America are obtainable from improvements in near-real-time precipitation observations for the region. In the longer term, improvements in precipitation forecast skill from dynamical models, like the fifth generation of the ECMWF seasonal forecasting system, will be essential in this effort.

Importance of Seasonality for the Response of a Mesic Temperate Grassland to Increased Precipitation Variability and Warming

Timing of precipitation events within the growing season and the non-uniformity of warming might be decisive for alterations in productivity and community composition, with consequences for ecosystem functioning. The responses of aboveground production, community composition, functional group and species evenness to altered intra-annual precipitation variability and their interactions with winter or summer warming were examined in European, mesic temperate grassland. Increased precipitation variability with an induced spring drought resulted in a 17% reduction in ANPP, and late drought reduced ANPP by 18% compared to regular rainfall patterns throughout the entire growing season. Winter warming increased ANPP by 12%, whereas summer warming showed no significant effect on biomass but decreased species richness. The effects of increased precipitation variability and warming on ANPP were independent of each other. Forbs benefited from high precipitation variability with spring drought events, likely due to reduced competitive pressure by decreasing, water stressed grasses. Increased precipitation variability coinciding with higher summer temperatures led to reduced species evenness and likely promoted the establishment of specialists and drought-tolerant species. Seasonality of climatic factors, here early versus late drought events in the high precipitation variability treatments, was important in driving shifts in community composition but not for decreases in ANPP. Non-uniform warming, here winter versus summer, affected the direction of response of both community composition and ANPP. Variability of resources is affecting ecosystem processes and species interactions. Recognition of seasonality and non-uniformity of climatic factors will improve predictions of plant performance and biotic interactions in response to climate change.

Inter- and Intra-annual precipitation variability and associated relationships to ENSO and the IOD in southern Africa

Precipitation variability at inter- and intra-annual scales may influence land-use management decisions in semi-arid savannas worldwide, and in particular, over the Kavango-Zambezi Transfrontier Conservation Area (KAZA) in southern Africa. Over KAZA, spatiotemporal precipitation variability forced by the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) is important to local and regional-scale decisions for planting, livestock grazing, and wildlife migration patterns. We investigate the annual water year (October–September) and early rainy season [October–November–December (OND)] precipitation patterns during 60 years before and after a 1970s shift in the global ocean–atmosphere system for this region in southern Africa. The coincidence of the number of wet (upper tercile) and dry (lower tercile) years and OND seasons during the various phases of ENSO and IOD are compared prior to (1950–1975) and after (1980–2008) the 1970s climate shift over KAZA. Since the 1970s climate shift, KAZA has been significantly drier and observed fewer wet years and OND seasons. ENSO is the dominant forcing of precipitation differences over southern Africa before and after the 1970s climate shift, with IOD playing a secondary role. However, when ENSO and IOD phases are analysed simultaneously, El Niño and positive IOD events are significantly related to dry periods. The forcing of atmospheric circulation over southern Africa before and after the 1970s climate shift during El Niño and La Niña events is significantly different. Prior to the 1970s climate shift, atmospheric circulation during El Niño (La Niña) favoured strong (weak) precipitation increases (decreases). Afterward the 1970s climate shift, atmospheric circulation during La Niña (El Niño) favoured strong (weak) precipitation decreases (increases). The shifting nature of climate modes, especially ENSO, and respective influence on rainfall variability for southern Africa is important to understand to better inform seasonal climate forecasts to improve operational decision-making for land-use and water management decisions in semi-arid savanna regions.

Agent-Based Simulation of Holocene Monsoon Precipitation Patterns and Hunter-Gatherer Population Dynamics in Semi-arid Environments

Based on archaeological evidence from Kutch-Saurashtra (N Gujarat, NW India), we use agent-based modelling (ABM) to explore the persistence of hunter-gatherer (HG) groups in semi-arid environments in the mid and late Holocene. Agents interact within a realistic semi-arid environment dominated by the monsoon. Precipitation trends are modelled from instrumental records (1871–2008) calibrated with existing models for the Asian monsoon in the Holocene (c. 12 ka–present). Experiments aim at exploring dependencies between population dynamics and climate-driven environmental change (in terms of resource availability) for precipitation patterns at the local, regional and continental scales. Resources are distributed across a simplified ground model. Average yearly precipitation (AYP, i.e. mean) and variance in yearly precipitation (VYP, i.e. standard deviation) are the main parameters affecting resource availability in the simulations. We assess the effects of environmental change on HG populations at different timescales: (1) patterns of seasonal (inter-annual) resource availability, (2) effects of changes in mean precipitation trends over the long (Pleistocene–Holocene) and the mid (Holocene, millennial) periods, and (3) effects of intra-annual precipitation variability, i.e. changes in standard deviation from mean precipitation trends over the short period (annual to decadal). Simulations show that (1) strong seasonality is coherent with the persistence of HG populations in India, independently of the geographical scale of the precipitation models, (2) changes in AYP over the mid period (Holocene) are not sufficient to explain the disappearance of HG populations in Kutch-Saurashtra (K-S) 4 ka and (3) precipitation variability (VYP) over the short period (annual to decadal) is the main parameter affecting population performance and overall ecosystem dynamics. To date, sufficiently refined palaeoclimatic records do not exist for the study area, but higher VYP values 4 ka do not exclude the possibility that other factors may have driven the disappearance of HG populations in Kutch-Saurashtra.

Water stress due to increased intra-annual precipitation variability reduced forage yield but raised forage quality of a temperate grassland

Due to climate change an increase in the intra-annual precipitation variability including extreme drought and heavy rainfall events is predicted to impact major ecosystem processes. Evidence suggests that crop and forage production will be affected by altered climate variability. Due to the growing human population and rising demand for high quality animal feed it is necessary to determine the consequence of increased precipitation variability on forage yield and quality in order to adapt or implement compensation strategies against possible negative effects.Here, we present data from a field experiment in which a temperate European grassland was subjected to altered intra-annual precipitation variability (low, medium, high) in interaction with management strategies namely fertilization and alteration of harvest date (delay by 10 days). We measured forage yield and root length, quantified parameters of forage quality (crude protein, crude fiber, crude ash, crude fat, sugar, neutral detergent fiber (NDF), acid detergent fiber (ADF), in vitro gas production) and estimated relative feed value, net energy for lactation and metabolizable energy. Additionally, we tested the influence of seasonality of extreme weather events on the responsiveness of forage yield and quality to management strategies.Increased intra-annual precipitation variability decreased forage yield of the grassland. Furthermore, the proportion of functional groups was altered toward less grass and more forb biomass with amplified precipitation variability. Increased crude protein content and reduced fiber content (crude fiber, NDF, ADF) with increasing precipitation variability improved the relative feed values. Crude protein content was enhanced by fertilization during drought but reduced by delayed harvest after the drought period. Fertilization reduced losses in grassland annual yield caused by extreme precipitation. Management strategies proved less effective if precipitation variability occurred later in the season than earlier in the season.A nitrogen dilution effect (decreased plant nitrogen concentration with increasing shoot biomass) likely influenced the grassland crude protein contents under altered precipitation regimes and might have masked possible effects of precipitation variability on plant nitrogen and therefore on quality of grassland species. Nevertheless, alterations in the plant community composition and plant senescence seem to be the main drivers of forage quality change. Fertilization during drought periods and harvest delay after drought periods were only partially successful as management strategies to sustain forage production in more extreme precipitation regimes of the future. Further strategies need to be developed that acknowledge the shift in plant species compositions as the main driver of changes in forage quality in the face of changing precipitation patterns.

Relationships of Fire and Precipitation Regimes in Temperate Forests of the Eastern United States

Abstract Fire affects virtually all terrestrial ecosystems but occurs more commonly in some than in others. This paper investigates how climate, specifically the moisture regime, influences the flammability of different landscapes in the eastern United States. A previous study of spatial differences in fire regimes across the central Appalachian Mountains suggested that intra-annual precipitation variability influences fire occurrence more strongly than does total annual precipitation. The results presented here support that conclusion. The relationship of fire occurrence to moisture regime is also considered for the entire eastern United States. To do so, mean annual wildfire density and mean annual area burned were calculated for 34 national forests and parks representing the major vegetation and climatic conditions throughout the eastern forests. The relationship between fire activity and two climate variables was analyzed: mean annual moisture balance [precipitation P − potential evapotranspiration (PET)] and daily precipitation variability (coefficient of variability for daily precipitation). Fire activity is related to both climate variables but displays a stronger relationship with precipitation variability. The southeastern United States is particularly noteworthy for its high wildfire activity, which is associated with a warm, humid climate and a variable precipitation regime, which promote heavy fuel production and rapid drying of fuels.

Linking vegetation response to seasonal precipitation in the Okavango–Kwando–Zambezi catchment of southern Africa

Understanding how intra-annual precipitation variability affects seasonal vegetation dynamics is critical for assessing the potential impacts of climate variability on vegetation structure and composition. This is important in semi-arid and arid ecosystems of southern Africa, where water is a limiting resource and timing of seasonal rainfall combined with the water storage capacity of different plant vegetation types affects remotely measured phenological cycles. Various lags and leads of savanna vegetation response to rainfall have been identified using remotely sensed data, but little attention has been given to vegetation greenness leading into the dry season. Vegetation production at the onset of the dry season interacts with the availability of water resources affecting fire dynamics, forage materials for wildlife and wildlife movement throughout the dry season. This is important for southern Africa as large proportions of the human population and economy are dependent on wildlife tourism. This study investigates the response of the end of the wet season vegetation production, as measured by Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) greenness, to the different months of wet season rainfall for different savanna vegetation types in a regional catchment of southern Africa. We estimated monthly precipitation using Tropical Rainfall Monitoring Mission 3B43 data and used MODIS 13A1 NDVI at a monthly time step for the years 2000–2009. Our model estimated greenness at the beginning of the dry season from the prior rainy season (October–April) precipitation using geographically weighted regression (GWR). The results show intra-annual wet season rainfall accounts for significant amounts of April NDVI variation. Overall intra-annual rainfall has a stronger effect for areas with greater proportions of grassland and dry, deciduous woodlands than for wetter, evergreen woodlands. These findings support previous research by highlighting the stronger association of grassland and open canopy woodlands to the end of the wet season monthly rainfall. This relationship is important for understanding seasonal precipitation effects on different savanna vegetation covers.

Hydro-geospatial analysis of ancient pastoral/agro-pastoral landscapes along Wadi Sana (Yemen)

In arid Southwest Arabia spatio-temporal patterning of land and water resources substantially shaped the lives and livelihoods of ancient peoples. This paper examines mid Holocene human subsistence and hydrology along the Wadi Sana drainage, including increased aridity, an associated shift from alluvial aggradation to incision, and its role the appearance of irrigation strategies that supplemented herding economies. Geospatial analyses indicate that (rather than solely the result of increased aridity) the onset of incision along middle Wadi Sana was most plausibly a function of heightened inter and intra-annual precipitation variability.

Effects of seasonal grazing and precipitation regime on the soil macroinvertebrates of a Mediterranean old-field

Soil macroinvertebrate communities (SMC) are well known to influence major ecosystem processes, but relatively few investigations have examined the mechanisms and factors involved in SMC regulation. We conducted a factorial experiment with combinations of seasonal grazing by sheep and irrigation (simulating different precipitation regimes) to assess their effects on the SMC of a semiarid Mediterranean old-field. We also analyzed effects on plant species richness, total aboveground biomass, and litter. The data were collected in autumn and spring, the two favorable seasons for SMC and primary production in the region, and season was included as an additional random factor. Main results were: 1) Ungrazed plots accumulated more aboveground plant biomass and litter during spring, providing extra food for soil biota. However, grazing during autumn or spring did not affect SMC characteristics. 2) Reduction of inter-annual precipitation variability in autumn and spring increased the abundance of two decomposer taxa: Oligochaeta and Diplopoda. Additionally, if summer drought was reduced, plant species richness, litter and the abundance of Isopoda were increased. 3) Oligochaeta and Diplopoda increase their abundance in spring, particularly, the most abundant taxon (Oligochaeta). We conclude that inter- and intra-annual variability in precipitation is a key environmental factor for the decomposer soil fauna in Mediterranean ecosystems, modifying the physical characteristics of the soils (humidity, hardness, etc.), as well as affecting the amount or characteristics of plant biomass or litter. The respiration system of the macroinvertebrates (cutaneous, tracheal or branquial) and the capacity to migrate vertically into the soil may determine the decomposers' responses to precipitation.