Prolonged Dry Periods Research Articles

Control of trace metal distribution and variability in an interdunal wetland

Trace elements are serious pollutants in the natural environment and are of increasing concern due to the adverse effects at global scale. To refine the current understanding of trace metal distribution and variability in natural environments, concentrations of dissolved trace metals (Ag, Al, As, B, Ba, Be, Co, Cr, Cd, Cu, Fe, Hg, Mo, Ni, Pb, Sb, Se, Th,Tl, U, V, Mn, Zn), major ions, inorganic nutrients (NO3, PO4), TOC and stable isotopes of water were determined in water samples from rainwater, seven piezometers and a pond in the coastal Doñana wetland during four sampling campaigns between 2017 and 2019. Results show clear evaporation signatures of stable isotopes in the pond but not in the groundwater. Hydrochemical analyses yield significant, systematic changes in groundwater trace metal and nutrient composition along the flowpath from the dune belt to the pond, controlled by organic matter in the sediments. Whereas major ions reached maximum concentrations in the pond due to evapoconcentration, most trace metals showed highest concentrations at sites with lower redox levels, except for B, As and U, which showed very high concentrations in the pond. Cu, Zn, Ni, Sb and Tl yielded higher median concentrations in rainwater than in most of the groundwater points and in case of Cu and Zn higher even than in surface water which points to an atmospheric input source of these elements. Temporal variability of trace metals was related to lower hydraulic heads after an elongated dry period which led to lower redox levels and higher concentrations of most of the trace elements whereas major ions showed more constant concentration levels. This is of special concern regarding climate change and the predicted higher frequency of prolonged dry periods, which could modify the natural hydrochemical patterns in undisturbed wetlands systems.

Microbial marker for seawater intrusion in a coastal Mediterranean shallow Lake, Lake Vrana, Croatia

Climate change-induced rising sea levels and prolonged dry periods impose a global threat to the freshwater scarcity on the coastline: salinization. Lake Vrana is the largest surface freshwater resource in mid-Dalmatia, while the local springs are heavily used in agriculture. The karstified carbonate ridge that separates this shallow lake from the Adriatic Sea enables seawater intrusion if the lakes' precipitation-evaporation balance is disturbed. In this study, the impact of anthropogenic activities and drought exuberated salinization on microbial communities was tracked in Lake Vrana and its inlets, using 16S rRNA gene sequencing. The lack of precipitation and high water temperatures in summer months introduced an imbalance in the water regime of the lake, allowing for seawater intrusion, mainly via the karst conduit Jugovir. The determined microbial community spatial differences in the lake itself and the main drainage canals were driven by salinity, drought, and nutrient loading. Particle-associated and free-living microorganisms both strongly responded to the ecosystem perturbations, and their co-occurrence was driven by the salinization event. Notably, a bloom of halotolerant taxa, predominant the sulfur-oxidizing genus Sulfurovum, emerged with increased salinity and sulfate concentrations, having the potential to be used as an indicator for salinization of shallow coastal lakes. Following summer salinization, lake water column homogenization took from a couple of weeks up to a few months, while the entire system displayed increased salinity despite increased precipitation. This study represents a valuable contribution to understanding the impact of the Freshwater Salinization Syndrome on Mediterranean lakes' microbial communities and the ecosystem resilience.

Demonstrating the potential of amberat middens for understanding late Quaternary palaeoenvironments in the Central Pilbara, western Australia

The Pilbara region in Western Australia (WA) is of high biological and archaeological significance, though our understanding of its environmental history is limited. Potentially valuable palaeoenvironmental archives exist throughout the Central Pilbara in caves and rockshelters in the form of amberat middens (crystallised animal urine), which are known from elsewhere to preserve botanical and faunal remains. Here we report a pilot study aimed at assessing how a multiproxy analysis of these middens could be used to infer past environmental change in response to climate change and therefore help to characterise the nature of past human-environmental relationships in the Pilbara region. Findings show that rockshelters of the inland Pilbara contain some of the oldest known amberat middens in Australia, extending fully back to the Last Glacial Maximum (LGM). Well preserved pollen and macrofossils in the middens tentatively suggest that vegetation throughout the late Pleistocene was likely dominated by an open woodland with a shift after 6000 BP to a more heterogenous pattern of vegetation with the increasing dominance of grassland communities. Several hiatuses in midden accumulation are apparent, which are tentatively interpreted as indicating that the region was affected by prolonged dry periods in the past. This may help explain concomitant patterns of decreased human occupation in the corresponding archaeological record. This pilot study has demonstrated the value of amberat middens for providing much needed local paleoenvironmental data in arid and semi-arid regions of Australia.

The technique for satellite monitoring of peatlands in order to determinate their fire hazard and combustion risks

Prolonged dry periods in spring and autumn, which are becoming more frequent for the Ukrainian Polissya, contribute to fires, especially in peatlands, that are dangerous for human health and ecosystems in general. Forecasting the risk of such natural and anthropogenic emergencies requires monitoring of current situations. Satellite monitoring provides an accurate information of the disaster and allows to realistically estimate the amount of damage. The article investigates the factors to be taken into account in peatlands monitoring and considers methods of processing of multispectral satellite data (Landsat, Sentinel series) in combination with traditional statistics data and field measurements. The technological diagram for making the studies is proposed. To assess the risks, the values that can be obtained simultaneously with the help of satellite data on large areas are determined: peat soil moisture, peat surface temperature, spectral indices (water, soil), evapotranspiration; the seasons of the greatest risks of fires are defined, and also risks associated with anthropogenic impact (proximity to settlements, agricultural trials, hayfields, careless handling of fire and arson). The condition of peatlands is diagnosed according to the developed criteria and assessed by four levels of fire risk - critical, high, low and insignificant. The study of spectral indices showed that with the help of the SAVI soil index in combination with the analysis of surface temperature, the burned areas and fires are accurately mapped in real-time. To predict the occurrence of fire situations, the use of two variants of the normalized differential water index (NDWI) in combination with thermal imaging is proposed. The test sites provide examples of diagnosing fires and burned areas in peatlands, as well as examples of forecasting fire hazards situations that require close attention of local authorities. Recommendations are given to prevent emergencies related to the burning of peatlands.

Soil water availability on biomass yield and water indicators of diverse warm-season perennial grasses in dryness conditions

Dryness triggers soil degradation processes and land abandonment in the south Mediterranean environment. Becoming unsuitable for food crops, it can be usable by low-iLUC risk biomass crops able to withstand prolonged dry periods due to drought-resilience traits and high biomass yield. The present experiment ascertained the biomass dry matter yield (DMY), water use efficiency (WUE) and water footprint (WF) by modulating soil water availability of six warm-season perennial grasses in the semiarid Mediterranean for two consecutive growing seasons. Two ecotypes of giant reed (Arundo donax L., ARCT and ARMO, respectively), one ecotype of African fodder cane (Saccharum spontaneum L. subsp. aegyptiacum (Willd.) Hack., SAC) and three hybrids of Miscanthus (the commercial M. × giganteus J.M. Greef, Deuter ex Hodk., Renvoize - M×G, and two new seed-based hybrids, GNT9 and GNT10, respectively) were subjected to 100%, 50% and 0% of maximum crop evapotranspiration (ETm) restoration supplied during summer months. Crop water use (CWU) differed among crops, growing seasons and irrigation regimes, and significantly influenced DMY, WUE and WF. ARCT, ARMO and SAC had higher DMY and WUE, and lower WF than Miscanthus hybrids. Among Miscanthus, the new seed-based hybrids outperformed the M×G in all examined parameters. Genotypic response in DMY, WUE and WF by varying the CWU had different trends and rates of change. The relationship between WUE and WF combining data of all genotypes, growing seasons and irrigation regimes followed an exponential decay; it underlined the importance to select for crops with high resource use efficiencies to reduce the water required per ton of biomass.

Lateral terrestrial water fluxes in the LSM of WRF‐Hydro: Benefits of a 2D groundwater representation

AbstractThe interactions between the atmosphere and the land surface are characterized by complex, non‐linear processes on varying time scales. The Noah‐MP is a medium complexity land‐surface model (LSM), which was recently selected as the new default LSM for the hydrologically enhanced Weather Research and Forecasting modelling system (WRF‐Hydro). Compared to its predecessor, several parameterizations were considerably improved and new ones added, inter alia more sophisticated groundwater descriptions, which aim to replace the traditional free‐drainage lower boundary condition. This study investigates the benefits that can be obtained from a two‐dimensional groundwater representation within the WRF‐Hydro modelling system by performing two offline simulations for the upper Danube river basin. In comparison to the free‐drainage reference simulation, the lateral routing of groundwater and the two‐way interaction with the water table greatly enhances small scale variability in simulated fields of soil moisture content and evapotranspiration (ET). The representation of upward fluxes from the aquifer helps to maintain higher soil moisture contents and thus ET during prolonged dry periods. These differences are rather small though (<2%) and explained by the fact that the study region is considered to be limited by radiative energy and not water availability. The most striking difference however is the performance gap in simulating streamflow. WRF‐Hydro with 2d groundwater scheme clearly outperforms the reference simulation in terms of performance metrics. A comparison with hourly streamflow observations for the water year of 2016 yields average Kling‐Gupta efficiencies of 0.79 versus 0.57 for the reference. Given that both model configurations were not calibrated beforehand, we conclude that the two‐dimensional groundwater option is especially beneficial for applications in poorly or even ungauged catchments. Furthermore, the inclusion of a so far missing compartment of the water cycle in the WRF‐Hydro modelling system allows for a more holistic representation of interactions between atmosphere land surface and subsurface, which will be advantageous in feedback studies with the fully coupled WRF‐Hydro.

Historical droughts in Irish catchments 1767–2016

AbstractRecent prolonged dry periods in summer 2018 and spring 2020 have reawakened interest in drought in Ireland, prompting questions regarding historical drought occurrence and potential long‐term risks. Employing 250 years of monthly precipitation and flow reconstructions, we investigate historical drought in Irish catchments evaluating the characteristics (number of events, duration, and deficits) of moderate, severe, and extreme droughts as well as the propagation of meteorological to hydrological drought. Using standardized indices, we identify three distinct catchment types. Cluster 1 catchments, located in the wetter northwest are characterized by small areas, low groundwater storage, and the highest frequency of hydrological drought relative to other catchments. Cluster 3 catchments, located in the drier east and southeast have larger areas, greater groundwater storage, the highest frequency of meteorological drought but the least hydrological droughts. However, once established, droughts in Cluster 3 tend to be more persistent with large accumulated deficits. Cluster 2 catchments, located in the southwest and west, are intermediate to Clusters 1 and 3, with hydrological droughts typically of shorter durations, reduced accumulated deficits but greater mean deficits. The most extreme droughts based on accumulated deficits across all catchments occurred in 1803–1806, 1854–1859, 1933–1935, 1944–1945, 1953–1954, and 1975–1977. Although not as severe, droughts in 1887–1888, 1891–1894, and 1971–1974 also appear as significant extremes. Changes in drought characteristics reveal a complex picture with the direction, magnitude, and significance of trends dependent on the accumulation period used to define drought, the period of record analysed, and the reference period used to standardize indices. Of particular note is a tendency towards shorter, more intense meteorological and hydrological droughts. Our findings offer important insight for drought and water management in Ireland given the paucity of extreme droughts in short observed river flow records.

Impact of Duration of Land Abandonment on Infiltration and Surface Runoff in Acidic Sandy Soil

Sandy soils are less fertile and, therefore, often abandoned in the Central European region. Land abandonment can cause the recovery of ecosystems by the replacement of crop species by vegetation that disperses from surrounding habitats and will be subsequently established (secondary succession). The objective of this study was to find the impact of secondary succession during more than 30 years of lasting abandonment of agricultural fields with acidic sandy soil on infiltration and surface runoff. The method of space-for-time substitution was used so that the fields abandoned at different times were treated as a homogeneous chronosequence. The impact of abandonment on infiltration and surface runoff was characterized by the changes in soil organic carbon content, pH, water and ethanol sorptivity, hydraulic conductivity, water drop penetration time, repellency index, time to runoff, and surface runoff coefficient. It was found that the abandoned soils previously subjected to agriculture showed a decrease in pH, a significant increase in soil water repellency, and a decrease in infiltration, which can lead to serious problems in terms of surface runoff and soil erosion. The pH(H2O) and pH(KCl) decreased monotonously and ethanol sorptivity did not change significantly during abandonment. The time to runoff did not change significantly between 10 and 30 years of abandonment, and it was not measured after 1 year of abandonment because no runoff occurred. The dependence of the other characteristics on the duration of field abandonment was not unambiguous. Water sorptivity and hydraulic conductivity showed a decrease between 1 and 10 years followed by a slight increase between 10 and 30 years of abandonment. On the other hand, soil organic carbon content, water drop penetration time, repellency index, and surface runoff coefficient showed an increase between 1 and 10 years followed by a slight decrease between 10 and 30 years of abandonment. To prevent soil water repellency and its consequences in sandy soils, an adequately high soil water content should be maintained, and mixed forest afforestation should be preferred to pine afforestation. This is extremely important in the context of climate change and the increasing frequency of prolonged dry periods.

Seed security among smallholder farmers in semi-arid Ghana

The Intergovernmental Panel on Climate Change's recent projections indicates that sensitivity to climate risks is likely to increase in the coming decades, with more erratic rainfall, prolonged dry periods, shorter growing seasons, and seed germination failures. The impacts of these risks on food, nutrition, and seed security among smallholder households are well-documented in literature. However, in the African context, the mechanisms through which the intersection of these ecological stressors and other factors affect seed security are poorly understood. We used a case study of semi-arid Ghana to examine seed security among smallholder farmers. We adopted a mixed-methods approach with intensive fieldwork in two farming villages. The study used multinomial logistic regression and qualitative interviews to understand how climatic and non-climatic factors determine seed security. Data collection methods included a household survey (n = 429), and in-depth interviews integrated with human-environment timelines (n = 20). Overall, the findings show that the significant determinants of seed security in semi-arid Ghana include village location, access to information, access to credit, and access to tractor plowing services. The results further showed that seed security is often disrupted by factors other than climate change, including farmer-herder conflicts, and the use of synthetic farming inputs. We found that some of the identified determinants are also evident in related food security studies. Ultimately, we argue that holistic efforts to resolving such factors is required to achieve both seed and food security among smallholders.

How Does Digitization Succeed in the Municipal Water Sector? The WaterExe4.0 Meta-Study Identifies Barriers as well as Success Factors, and Reveals Expectations for the Future

Water is increasingly taking center stage when it comes to coping with climate change. Especially in urban areas, negative consequences from heavy rainfall events and prolonged dry periods are rising worldwide. In the past, the various tasks of urban water management were performed by different departments that often did not cooperate with each other (water supply, wastewater disposal, green space irrigation, etc.), as the required water supply was not a question of available water volumes. This is already changing with climate change, in some cases even dramatically. More and more, it is necessary to consider how to distribute available water resources in urban areas, especially during dry periods, since wastewater treatment is also becoming more complex and costly. In the future, urban water management will examine water use in terms of its various objectives, and will need to provide alternative water resources for these different purposes (groundwater, river water, storm water, treated wastewater, etc.). The necessary technological interconnection requires intelligent digital systems. Furthermore, the water industry must also play its role in global CO2 reduction and make its procedural treatment processes more efficient; this will also only succeed with adequate digital systems. Although digitization has experienced an enormous surge in development over the last five years and numerous solutions are available to address the challenges described previously, there is still a large gap between the scope of offerings and their implementation. Researchers at Hof University of Applied Sciences have investigated the reasons for this imbalance as part of WaterExe4.0, the first meta-study on digitization in the German-speaking water industry, funded by the German Federal Ministry of Education and Research. Only 11% of roughly 700 identified products, projects and studies relate to real applications. For example, the surveyed experts of the water sector stated that everyday problems are considered too little or hardly at all in new solutions, which greatly overburdens users. Furthermore, they see no adequate possibility for a systematic analysis of new ideas to identify significant obstacles and to find the best way to start and implement a digitization project. The results from four methodologically different sub-surveys (literature and market research, survey, expert interviews and workshops) provide a reliable overview of the current situation in the German-speaking water industry and its expectations for the future. The results are also transferable to other countries.

Assessment of Groundwater Quality Using Water Quality Index and Geographic Information System in Kumbotso Local Government Area, Kano State, Nigeria

Water managers are faced with issues of groundwater resources management in dry land environments characterized by increasing population growth and prolonged dry period. Pollution of such resources has become a problem of notable importance in many arid and semi-arid environments of the developing countries. Unplanned urbanization; industrialization coupled with an increase in agricultural expansion has adversely affected groundwater quality. This study provides an overview of the status of groundwater quality in Kumbotso L.G.A using Water Quality Index. Physico-chemical parameters of pH, total dissolved solids, total hardness, magnesium, chloride, nitrate, calcium, and sulphate were measured from 12 groundwater samples. The results of the analysis were compared to the WHO standards to ascertain conformity with the guidelines. The Geographic Information System (GIS) was employed for mapping the distribution of various quality parameters as well as the overall groundwater quality condition. The overall map produced shows that 53.42km2 of the study area representing 33.81% were of excellent quality while 104.58km2 representing 66.19% of the area was found to be of good quality. Thus, a GIS based map developed can be a useful practical tool by water managers, policymakers and concerned communities in taking strategic decisions towards effective management of groundwater in the study area.

Sources of stream base flow in blanket peat covered catchments

A two year hydrological characterisation programme of relatively intact blanket peat-covered catchments, underlain by geochemically distinct substrates, investigated the influence of sub-peat materials on the runoff regimes of the first order and second order streams draining them. Semi-continuous monitoring of flow and water quality revealed a strong inverse relationship between stream flow rates and specific electrical conductance (SEC), with runoff chemistries during storm flow proving comparable in all three catchments. By contrast, differences in water quality between catchments became more pronounced at lower flow, where increased ion concentrations in stream water reflected reactions with peat substrate materials. Water table monitoring in peat at all three sites revealed groundwater levels to vary by less than 0.6 m over the investigation period. Findings suggest runoff consists of near constant inputs of higher specific electrical conductance peat substrate discharge, mixing with variable proportions of less mineralised and more compositionally variable bog water. Although making up less than 5% to total runoff, the contribution of more mineralised waters plays an important role in maintaining stream flow, particularly during prolonged dry periods, and may help explain the aquatic biodiversity encountered in blanket peat covered areas.

IMPACT OF PROLONGED DRY PERIOD ON OIL PALM YIELD AND MILL EXTRACTION RATIO: A CASE STUDY

Based on current trends in climate change, El Nino and La Nina events are likely to become more frequent, with the former having a more significant negative impact on oil palm growth and production. Since 1980, ten El Nino events or prolonged dry periods have been recorded in Indonesia, of which three and five events have been categorised as severe and moderate, respectively. The most severe of the three El Nino events occurred in 1997, followed by a more recent one in 2015. This paper is a case study which examines the impact of the 2015 El Nino event on the fresh fruit bunch (FFB) production of two generations of oil palms planted in two neighbouring estates and oil extraction ratios (OER) of a mill receiving crop from the latter two estates. Four consecutive months of low rainfall in 2015, resulted in annual water deficits of 280 - 313 mm, which was followed by a decline in FFB production over two distinct periods i.e. 4 to 12 months and 24 to 30 months after the El Nino event, respectively. In both cases, a sharp decline in the number of harvestable bunches was the main contributing factor, likely to be due to an increase in inflorescence abortion and lowering of inflorescence sex-ratio. Average bunch weight (ABW) generally remained unaffected. The initial impact of the drought was more severe on the younger palms, but due to a better recovery rate, the overall yield decline (23%) over a 12-month period in the following year, was significantly lower than in older palms (30%). Analysis of 14 years’ yield and climatic data showed that apart from rainfall, other abiotic and biotic factors such as fruiting activity may also be contributing to the 3-year production cycles (peak crop, decline, recovery, peak crop) exhibited by both estates. As such, it was difficult to accurately apportion yield decline primarily due to water deficit from the other influencing factors. The study also indicated a negative effect of drought on mill OER. Extended dry periods in 2015 (4 months) and 2019 (4 months) were consistently correlated with periods of declining OER, 7 to 14 months later. Like FFB, the prolonged decline could also be attributed to multiple factors. Keywords: El Nino, oil palm, OER, rainfall, water deficit.

Attribution of the role of climate change in the forest fires in Sweden 2018

Abstract. In this study, we analyse the role of climate change in the forest fires that raged through large parts of Sweden in the summer of 2018 from a meteorological perspective. This is done by studying the Canadian Fire Weather Index (FWI) based on sub-daily data, both in reanalysis data sets (ERA-Interim, ERA5, the Japanese 55 year Reanalysis, JRA-55, and Modern-Era Retrospective analysis for Research and Applications version 2, MERRA-2) and three large-ensemble climate models (EC-Earth, weather@home, W@H, and Community Earth System Model, CESM) simulations. The FWI, based on reanalysis, correlates well with the observed burnt area in summer (r=0.6 to 0.8). We find that the maximum FWI in July 2018 had return times of ∼24 years (90 % CI, confidence interval, > 10 years) for southern and northern Sweden. Furthermore, we find a negative trend of the FWI for southern Sweden over the 1979 to 2017 time period in the reanalyses, yielding a non-significant reduced probability of such an event. However, the short observational record, large uncertainty between the reanalysis products and large natural variability of the FWI give a large confidence interval around this number that easily includes no change, so we cannot draw robust conclusions from reanalysis data. The three large-ensembles with climate models point to a roughly 1.1 (0.9 to 1.4) times increased probability (non-significant) for such events in the current climate relative to preindustrial climate. For a future climate (2 ∘C warming), we find a roughly 2 (1.5 to 3) times increased probability for such events relative to the preindustrial climate. The increased fire weather risk is mainly attributed to the increase in temperature. The other main factor, i.e. precipitation during summer months, is projected to increase for northern Sweden and decrease for southern Sweden. We, however, do not find a clear change in prolonged dry periods in summer months that could explain the increased fire weather risk in the climate models. In summary, we find a (non-significant) reduced probability of such events based on reanalyses, a small (non-significant) increased probability due to global warming up to now and a more robust (significant) increase in the risk for such events in the future based on the climate models.

Rapid loss of biomass and viability of air-exposed food reserve tubers from a dynamic wetland system in Mozambique

Climate change is already affecting East Africa. This includes the Banhine area, the driest region in Mozambique, but with a steadily increasing population. In favourable times people live from subsistence farming, which depends on rainfall. However, during prolonged dry periods when crops fail they depend on wild plant reserves such as Bolboschoenus glaucus tubers. Larger areas of surface-exposed tubers of this key plant species have been found in the Banhine area, probably dug up by burrowing animals. With the intention of imitating increasingly long periods of drought, we investigated the consequences when B. glaucus tubers are moved upwards from the substrate in an empirical greenhouse experiment. We observed that once brought up from the soil substrate, these storage organs rapidly lose mass and do not retain their vitality even for half a year. Our findings imply that these tubers are best kept in situ. The lack of resistance of these edible plants to disturbances in dry climate conditions can have serious consequences for emergency food supply of local populations and animals. Therefore, follow-up studies are warranted and awareness should be raised.

Carbon dioxide fluxes and carbon balance of an agricultural grassland in southern Finland

Abstract. A significant proportion of the global carbon emissions to the atmosphere originate from agriculture. Therefore, continuous long-term monitoring of CO2 fluxes is essential to understand the carbon dynamics and balances of different agricultural sites. Here we present results from a new eddy covariance flux measurement site located in southern Finland. We measured CO2 and H2O fluxes at this agricultural grassland site for 2 years, from May 2018 to May 2020. In particular the first summer experienced prolonged dry periods, which affected the CO2 fluxes, and substantially larger fluxes were observed in the second summer. During the dry summer, leaf area index (LAI) was notably lower than in the second summer. Water use efficiency increased with LAI in a similar manner in both years, but photosynthetic capacity per leaf area was lower during the dry summer. The annual carbon balance was calculated based on the CO2 fluxes and management measures, which included input of carbon as organic fertilizers and output as yield. The carbon balance of the field was −57 ± 10 and −86 ± 12 g C m−2 yr−1 in the first and second study years, respectively.

Climate Variability May Delay Post-Fire Recovery of Boreal Forest in Southern Siberia, Russia

Prolonged dry periods and increased temperatures that result from anthropogenic climate change have been shown to increase the frequency and severity of wildfires in the boreal region. There is growing evidence that such changes in fire regime can reduce forest resilience and drive shifts in post-fire plant successional trajectories. The response of post-fire vegetation communities to climate variability is under-studied, despite being a critical phase determining the ultimate successional conclusion. This study investigated the responses of post-fire recruited species to climate change and inter-annual variability at 16 study sites that experienced high-severity fire events, mostly in early 2000, within the Scots pine forest-steppe zone of southeastern Siberia, Russia. These sites were originally dominated by Scots pine, and by 2018, they were recruited by different successional species. Additionally, three mature Scots pine stands were included for comparison. A Bayesian Additive Regression Trees (BART) approach was used to model the relationship between Landsat-derived Normalized Difference Vegetation Index (NDVI) time series, temperature and precipitation in the 15 years after a stand-replacing fire. Using the resulting BART models, together with six projected climate scenarios with increased temperature and enhanced inner-annual precipitation variability, we simulated NDVI at 5-year intervals for 15 years post-fire. Our results show that the BART models performed well, with in-sample Pseudo-R2 varying from 0.49 to 0.95 for fire-disturbed sites. Increased temperature enhanced greenness across all sites and across all three time periods since fires, exhibiting a positive feedback in a warming environment. Repeatedly dry spring periods reduced NDVI at all the sites and wetter summer periods following such dry springs could not compensate for this, indicating that a prolonged dry spring has a strong impact consistently over the entire early developmental stages from the initial 5 years to 15 years post-fire. Further, young forests showed higher climate sensitivity compared to the mature forest, irrespective of species and projected climatic conditions. Our findings suggest that a dry spring not only increases fire risk, but also delays recovery of boreal forests in southern Siberia. It also highlights the importance of changing rainfall seasonality as well as total rainfall in a changing climate for post-fire recovery of forest.

Improving Irrigation Water Use Efficiency of Robusta Coffee (Coffea canephora) Production in Lam Dong Province, Vietnam

Recent prolonged dry periods and lack of irrigation water have severely affected the productivity of coffee farms in the Central Highlands of Vietnam. This paper analyzes the efficiency of irrigation water use for Robusta coffee (Coffea canephora) in the Lam Dong province. A Cobb–Douglas production function was used to determine coffee productivity’s response to the application of irrigation water and other production factors using data collected from 194 farmers, while the technical efficiency (TE) and irrigation water use efficiency (IWUE) were analyzed using a data envelopment analysis (DEA) model. The correlation of different factors to IWUE was determined using the Tobit model. The production function analysis using Cobb–Douglas shows that the volume of irrigation water, amount of working capital, labor, and farm size significantly influence coffee productivity. Indigenous farmers are more efficient in utilizing irrigation water than migrant farmers. The Tobit result indicates that farmers’ experience, education level, the distance of farm to water sources, security of access to water sources, extension contact, and credit access significantly affect IWUE. The study findings further suggest that mitigating water shortages in coffee farms require subregional and national policy support such as better access to credit and extension services, training, land management, and household-level efforts to improve farming practices through the application of appropriate technologies and traditional knowledge.

Soil Moisture Behavior in Relation to Topography and Land Use for Two Andean Colombian Catchments

Understanding the soil moisture behavior in relation to land use in tropical Andean mountain catchments is essential for comprehending water fluxes, ecohydrological relations and hydrological dynamics in this understudied ecosystem. Soils are a key factor of these ecosystems, especially in reference to water level regulation and anthropogenic activities that can alter the interactions, and generate physical, chemical and biological imbalances. In this study, we investigated the relationship between precipitation, soil water content (SWC) and the flow at different pedon scales, and hillslope and microcatchment scales subjected to different land uses. The results showed the relation between the soils uses, topographical conditions and soil moisture at the microcatchment scale. At the pedon scale, soil moisture is higher and with a low variability in depth; high soil moisture content throughout the study period was registered in forest > pasture > coffee agroforestry systems. The topographic wetness index (TWI), despite its adjusted interpretation of the behavior of humidity at the microcatchment scale, is a poor predictor of the behavior of soil humidity at the pedon scale. Pedon water content has a close relation with the precipitation behavior, especially in prolonged dry and humid periods. The soils studied tend to present udic moisture regimes with a dry period of approximately 67 accumulative days per year. The mean flow behavior responds to precipitation and soil moisture behavior at a monthly scale. Understanding the consequences of the land cover changes in relation to soil water behavior, as well as how soil water interacts with the different components of the hydric balance at different scales, allows an understanding of the complex interactions in natural microcatchments under different land use systems.

Analysis of spatial and temporal changes of RUSLE-K soil erodibility factor in semi-arid areas in two different periods by conditional simulation

ABSTRACT Soil erosion is the most important soil degradation process threatening semi-arid and arid areas. In this study, the change in the RUSLE-K soil erodibility values due to changed climatic conditions over a 10-year period was used as a tool to investigate soil erosion potential with Sequential Gaussian Simulation (SGS) method in the Mogan catchment in Turkey. For this purpose, soil erodibility values were determined for soil samples taken from the same coordinates in 2000 and 2010, and erosion susceptibility distribution maps were produced. The results showed that even though land use practices remained unchanged, soil erodibility values changed spatially and temporally, with the relationship dependent on climatic factors. More specifically, the effects of decreased precipitation, exacerbated by increased evaporation and more prolonged dry periods, made some areas in the catchment more susceptible to erosion. The vulnerability soils in the catchment increased markedly, with the area classified as subject to ‘very severe erodibility’ increasing more than threefold, from 762 ha to 2477 ha. This study has reinforced the need for ‘minimal disturbance’ land use, supplemented by monitoring that incorporates meteorological and soil test data, to minimize soil erosion and maximize the sustainability of agricultural activities in semi-arid and arid areas.