Prolonged Drought Periods Research Articles

Repeated century-scale droughts over the past 13,000 yr near the Hudson River watershed, USA

Long-term sediment and ground-penetrating radar data from Davis Pond, a small lake near the Hudson River valley, reveal past droughts in a historically humid region that presently supplies water to millions of people in and around New York City. A minimum of eleven sandy paleoshoreline deposits in the lake date from 13.4 to 0.6 cal ka BP. The deposits span 1500 to 200 yr between bracketing radiocarbon ages, and intrude into lacustrine silts up to 9.0 m below the modern lake surface in a transect of six sediment cores. Three low stands, ca. 13.4–10.9, 9.2 and 8.2 cal ka BP indicate low regional moisture balance when low temperatures affected the North Atlantic region. Consistent with insolation trends, water levels rose from ca. 8.0 cal ka BP to present, but five low stands interrupted the rise and are likely associated with ocean–atmosphere interactions. Similar to evidence from other studies, the data from Davis Pond indicate repeated multi-century periods of prolonged or frequent droughts super-imposed on long-term regional trends toward high water levels. The patterns indicate that water supplies in this heavily populated region have continuously varied at multiple time scales and confirm that humid regions such as the northeastern United States are more prone to severe drought than historically expected.

Indian and Pacific Ocean Influences on Southeast Australian Drought and Soil Moisture

Abstract The relative influences of Indian and Pacific Ocean modes of variability on Australian rainfall and soil moisture are investigated for seasonal, interannual, and decadal time scales. For the period 1900–2006, observations, reanalysis products, and hindcasts of soil moisture during the cool season (June–October) are used to assess the impacts of El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) on southeastern Australia and the Murray–Darling Basin, two regions that have recently suffered severe droughts. A distinct asymmetry is found in the impacts of the opposite phases of both ENSO and IOD on Australian rainfall and soil moisture. There are significant differences between the dominant drivers of drought at interannual and decadal time scales. On interannual time scales, both ENSO and the IOD modify southeastern Australian soil moisture, with the driest (wettest) conditions over the southeast and more broadly over large parts of Australia occurring during years when an El Niño and a positive IOD event (La Niña and a negative IOD event) co-occur. The atmospheric circulation associated with these responses is discussed. Lower-frequency variability over southeastern Australia, however, including multiyear drought periods, seems to be more robustly related to Indian Ocean temperatures than Pacific conditions. The frequencies of both positive and negative IOD events are significantly different during periods of prolonged drought compared to extended periods of “normal” rainfall. In contrast, the frequency of ENSO events remains largely unchanged during prolonged dry and wet periods. For the Murray–Darling Basin, there appears to be a significant influence by La Niña and both positive and negative IOD events. In particular, La Niña plays a much more prominent role than for more southern regions, especially on interannual time scales and during prolonged wet periods. For prolonged dry (wet) periods, positive IOD events also occur in unusually high (low) numbers.

Impact of drought on wildland fires in Greece: implications of climatic change?

An increasing trend and a statistically significant positive correlation between wildfire occurrence, area burned and drought (as expressed by the Standardized Precipitation Index, SPI) have been observed all over Greece, during the period 1961–1997. In the more humid and colder regions (Northern and Western Greece) the number of fires and area burned were positively correlated to both summer (SPI6_October) and annual drought (SPI12_September), whereas in the relatively more dry and hot regions (Southern and Central Greece) the number of fires and area burned were correlated only to summer drought. In 1978, Greece entered a period of prolonged drought, possibly as a result of the global climatic change. Data analysis of the period 1978–1997 revealed a statistically significant increase in the mean annual number of fires, the area burned and the summer and annual drought episodes in the relatively more humid and colder regions (Northern and Western) of Greece (which in the past were characterized by less fires and area burned) compared to the more dry and hot regions (Southern and Eastern Greece), which always presented high fire activity. Additionally, analyzing the two sub-periods (1961–1977, 1978–1997) separately, drought was significantly correlated only to fire occurrence during the years 1961–1977, whereas during 1978–1997 drought was significantly correlated mainly to area burned. It became obvious that drought episodes, although they are not solely responsible for fire occurrence and area burned, they exert an increasingly significant impact on wildfire activity in Greece.

Acacia longifolia invasion impacts vegetation structure and regeneration dynamics in open dunes and pine forests

Acacia spp. are among the most serious plant invaders worldwide, and Acacia longifolia specifically causes problems in Portugal. In this study, we evaluated the impacts of A. longifolia invasion on community structure, light climate, plant diversity and regeneration in pine forests and open stabilized dunes in northern and southern Portugal. Having the growth form of a small tree or shrub, between 1 and 8 m tall, A. longifolia tended to dominate the middle stratum of forests and to share dominance in the upper stratum of open dunes. The presence of A. longifolia was associated with a decreased canopy cover in the lower stratum of all studied habitats, and at some sites with a significantly increased leaf area index and reduced light intensity in the understory. Species number and diversity were reduced in some habitats by up to 50% in invaded compared to non-invaded areas. Furthermore, in forest habitats, A. longifolia seedlings were facilitated by proximity to an adult A. longifolia while the establishment and growth of native seedlings was negatively impacted. The replacement of drought tolerant native species by the water spending invader, A. longifolia, may have serious implications for ecosystem functioning, especially during the prolonged drought periods predicted to occur in Portugal in the future.

Influence of intermittent estuary outflow on coastal sediments of adjacent sandy beaches

Outflows from estuaries potentially contribute to the productivity of adjacent coastal waters, although most previous work has been on estuaries with considerable river discharge. We investigated the influence of estuary outflow on aspects of coastal sediments adjacent to two seasonally intermittent estuaries, the Curdies and Anglesea Rivers, in southwest Victoria, Australia. For each estuary, we measured sediment organic matter, microphytobenthic chlorophyll a and microbial utilization of carbon sources at three locations associated with each estuary: (1) inside estuary mouth, (2) estuary swash and (3) control swash (an open beach distant from any estuarine influences). Sampling occurred one week before and at one and nine weeks after both an artificial mouth opening and a separate natural flood at both estuaries. Significant temporal changes were detected for all three variables at the estuary mouth and estuary swash but the direction of change was inconsistent across the two estuaries and between the artificial mouth opening and natural flood. Organic matter in both estuaries showed no difference after the artificial mouth openings. Only Anglesea showed an increase in organic matter in the estuary mouth and estuary swash after the floods. Microphytobenthic chlorophyll a concentrations were highest when the estuary mouths were closed. Concentrations decreased at all locations at Curdies after the mouth was artificially opened. The estuary mouth at Anglesea sustained high chlorophyll concentrations and the estuary swash increased one week post artificial opening. The flood event resulted in an increase in chlorophyll a at the estuary mouth and swash at both estuaries, one week post flood. At Curdies, the microbial utilization of different carbon sources changed after both mouth events; estuary mouth and estuary swash showed similar patterns at one and nine weeks post opening. At Anglesea, the bacteria utilized different carbon sources between locations and the only significant interaction between location and time was post flood with change in carbon sources utilized by bacteria in the estuary mouth and estuary swash for one and nine weeks post flood. The southern coastline of Australia is characterized by estuaries with small catchments. This study highlights the spatial and temporal variability in the effects of the output of relatively small, intermittent estuaries on coastal sediment of adjacent beaches, particularly during prolonged periods of drought.

Secondary production and biomass of Cladocera in marginal lakes after the recovery of their hydrologic connectivity in a river–reservoir transition zone

Secondary production and biomass of Cladoceran populations were studied in two marginal lakes whose connections to a tropical river were re-established after a prolonged drought period. This study investigates the process of the recovery of the cladoceran populations after the hydrologic reconnection with the river was established. It also compares the energetic dynamic of Cladoceran populations in two lakes, one with a wide and another with a narrow connection to the river. Samples were collected every 48 h for 1 month, immediately after the river water inflow to the lakes, and 7 months after the reconnection with the river during a period of hydrologic stability of the lakes. Secondary production and biomass were compared between lakes and periods, to identify the main controlling factors for the observed variations in Cladoceran productivity. Cladocerans were more productive during the rainy period, immediately after the increased water volume, when high water temperatures were recorded in the two lacustrine systems. Secondary production and biomass values were higher in the more eutrophic lake, wherein the water chemical and physical characteristics presented slow alterations during the rainy period. Although the lake with large spatial heterogeneity and linkages with the river exhibited high Cladoceran richness, the secondary production and biomass were low. Variations in water volumes and temperatures and changes in trophic status affected the secondary production and biomass of the main Cladoceran species in the two studied lakes.

Phosphorus release from forest harvesting on an upland blanket peat catchment

The aim of this study was to investigate the release of phosphorus (P) to receiving waters resulting from harvesting 34-year-old lodgepole pine trees in an upland peat catchment. The study site was within a 25.3-hectare (ha) area, and was drained by a stream that received flows from ploughed furrows, mainly, via collector drains, and discharged directly to the salmonid Shrahrevagh River, Burrishoole, Co. Mayo, Ireland. The study site was divided into two parts: the upstream part was left intact and the downstream part was harvested in early Autumn 2005 following implementation of forest guidelines. Good management practices such as proper use of brash mats and harvesting only in dry weather were implemented. Two instrumented stations were established – one just upstream (US) and the other just downstream (DS) of the clearfelled area. The measurement of P concentrations at the two stations commenced in May 2005, two months before the harvesting started. The daily mean P concentration at the DS station increased from about 6 μg L −1 of total reactive phosphorus (TRP) during pre-clearfelling to 429 μg L −1 in August 2006. By October 2009, four years after clearfelling, the P concentrations at the DS station had returned to pre-clearfelling levels. In the first three years after harvesting, up to 5.15 kg ha −1 of TRP was released from the harvested catchment to the receiving water; in the second year alone, 2.3 kg ha −1 of TRP was released. Linear regression can be used to describe the relationship between TRP load and water discharge. About 80% of the total phosphorus (TP) in the study stream was soluble and more than 70% of the P release occurred in storm events, indicating that traditional buffer strips with widths of 15–20 m might not be efficient for P immobilization. The P concentrations were affected by antecedent weather conditions and highest concentrations occurred during storm events following prolonged drought periods. The water extractable phosphorus (WEP) contents in the soil were significantly higher below windrow/brash material than in brash-free areas, and whole-tree harvesting should be studied as one of the means to decrease P export from blanket peats.

Drying–rewetting events reduce C and N losses from a Norway spruce forest floor

Periods of prolonged summer drought are likely to be expected for this century, with possibly strong effects on carbon (C) and nitrogen (N) mineralization in soils. Drought generally reduces mineralization rates, but the possibility of excess mineralization pulses during rewetting raises the question about the net effect of drying–rewetting events. In this experiment, we measured C and N mineralization in undisturbed soil columns that were either kept under continuously moist conditions (control) or that were subjected to drying-rewetting. We had three treatments (D1–D3) with different drying intensity (increasing from D1 to D3) but uniform rewetting intensity (4 mm d −1). Soil columns were taken from a Norway spruce forest in Bavaria, Germany. The CO 2 fluxes from control and treatment groups were identical before drying. Over the 80 d drought period, total CO 2 emissions from D1, D2, and D3 were only 72, 52 and 43% of that from the control, respectively. Rewetting resulted in a fast increase of CO 2 fluxes to approx. the same level as in the control. Rewetting could not restore soil moisture of the dry soil to the level of the control, presumably because of preferential flow and water repellency of soil organic matter. No significant excess C mineralization during the 40 d rewetting period was observed. Adding up total CO 2 fluxes during drought and rewetting period, the treatments D1, D2, and D3 emitted only 88, 71 and 67% of the CO 2 emitted by the control. Measurements of dissolved organic carbon (DOC) did only show minor differences between control and treatment columns, indicating that no significant accumulation of DOC took place during the drought period. Radiocarbon signature of emitted CO 2 indicated that C mineralization was reduced with decreasing water availability and no new substrate became bioavailable. Net N mineralization over the course of the whole experiment was reduced by drought to 77, 65 or 52% of the control. Net nitrification was virtually zero during drought whereas net ammonification continued at reduced levels. In summary, we found that drying–rewetting generally reduced C and N mineralization in this soil and that the total reduction increased with drought intensity.

Surfactants Increase Uniformity of Soil Water Content and Reduce Water Repellency on Sand-Based Golf Putting Greens

Abstract Water repellency and related localized dry spots are common problems on sand-based root zones often used for golf putting greens. The objective of this study was to quantify the effect of three commonly used surfactants applied to a sand-based root zone on turfgrass visual quality and drought symptoms, soil water content and uniformity, and soil water repellency. In 2007 and 2008, a study was conducted in Wisconsin on a creeping bentgrass golf putting green with a water-repellent sand soil. Prolonged periods of drought occurred in both years. Treatments included three surfactants and two controls, one irrigated at 30% of potential evapotranspiration (ETp) and a second irrigated at 100% of ETp. The surfactant treatments were irrigated at 30% of ETp. Soil moisture was measured weekly in each plot on a 5 × 5 30-cm grid pattern, along with visual estimates of area exhibiting drought symptoms and turfgrass visual quality. Soil water repellency was measured before and at the conclusion of each growing season. In 2007, the surfactant treatments maintained visual quality lower than the well-irrigated control treatment but greater than the reduced-irrigation control treatment. In 2008, substantial drought symptoms appeared on all surfactant treatments, which recovered faster than the reduced-irrigation control treatment. Soil water contents of surfactant treatments were similar to each other and the reduced-irrigation control on most testing dates. During periods of drought, surfactant-treated soils had the greatest uniformity of moisture content and lowest water repellency at the end of each growing season. These results indicate that use of these surfactants can reduce water use while improving visual quality compared with untreated areas, prevent localized dry-spot development, and increase moisture uniformity in sand-based golf putting green root zones.

Potential shift in tree species composition after interaction of fire and drought in the Central Alps

The future trajectory of forest ecosystems under climate change is heavily debated. Previous studies on the impacts of climate change on forest ecosystems have focused mainly on direct effects of altered climatic conditions, whereas interactions with disturbance events have been largely neglected. The aim of this study is to explore interactions of drought with fire disturbance and to assess their effects on tree species shifts in the European Central Alps. Tree recruitment after a stand replacing wildfire in the Rhone valley, Switzerland, was measured along an altitudinal temperature moisture gradient. Recruitment was more successful in pioneer species (Betula pendula, Populus tremula and Salix appendiculata) than in pre-fire stand forming (PFSF) species (Larix decidua, Picea abies and Pinus sylvestris). Seedling and sapling density was not related to fire intensity, but it correlated with the distance to the forest edge in PFSF species. The window of opportunity for seedling establishment was short (1–2 years), and moisture deficit was the main limiting factor for tree recruitment at lower altitudes. We suggest that prolonged drought periods, as projected under continued global warming, will further aggravate tree recruitment success after fire disturbance at low altitudes of the Central Alps and may eventually lead to a shift from PFSF species to either more drought-tolerant species or to forest-free vegetation.

Application of linear stochastic models for drought forecasting in the Büyük Menderes river basin, western Turkey

In the present study, a seasonal and non-seasonal prediction of the Standardized Precipitation Index (SPI) time series is addressed by means of linear stochastic models. The methodology presented here is to develop adequate linear stochastic models known as autoregressive integrated moving average (ARIMA) and multiplicative seasonal autoregressive integrated moving average (SARIMA) to predict drought in the Buyuk Menderes river basin using SPI as drought index. Temporal characteristics of droughts based on SPI as an indicator of drought severity indicate that the basin is affected by severe and more or less prolonged periods of drought from 1975 to 2006. Therefore, drought prediction plays an important role for water resources management. ARIMA modeling approach involves the following three steps: model identification, parameter estimation, diagnostic checking. In model identification step, considering the autocorrelation function (ACF) and partial autocorrelation function (PACF) results of the SPI series, different ARIMA models are identified. The model gives the minimum Akaike Information Criterion (AIC) and Schwarz Bayesian Criterion (SBC) is selected as the best fit model. Parameter estimation step indicates that the estimated model parameters are significantly different from zero. Diagnostic check step is applied to the residuals of the selected ARIMA models and the results indicated that the residuals are independent, normally distributed and homoscedastic. For the model validation purposes, the predicted results using the best ARIMA models are compared to the observed data. The predicted data show reasonably good agreement with the actual data. The ARIMA models developed to predict drought found to give acceptable results up to 2 months ahead. The stochastic models developed for the Buyuk Menderes river basin can be employed to predict droughts up to 2 months of lead time with reasonably accuracy.

Late Chalcolithic/Early Bronze I Transition Settlements in the Middle Jordan Valley: Investigating Alluvial Sequences as a Chronostratigraphical Framework, and Cycles as a Social Organising Component

Recent palaeoenvironmental and archaeological data from the Middle Jordan Valley give evidence of important geomorphic modifications during the Late Chalcolithic and the early beginning of the Bronze Age. Significant human settling/ resettling activities were also identified during this period and found to be concurrent with these modifi cations. A major phase of cutting-down, followed by the development of wide floodplains at the foot of escarpments and on the banks of the Wadi Zarqa, appears to mark the chronological limit between settlements displaying the classic Late Chalcolithic “ Ghassulian” culture material, and others from the Late Chalcolithic/ Early Bronze I (EBI) horizon. Some sites of “ pure Ghassulian” culture might have coexisted with the new settlements and their mixed culture material. These changes in the natural and cultural landscapes of the study region were preceded by a period of prolonged drought, which might have been the regional expression of the worldwide cold and dry event of around 5500 14C BP.

GROUNDWATER EXTRACTION MODELLING FOR KUALA LUMPUR WATER RESOURCE PLANNING

Portable water consumption in Kuala Lumpur and the surrounding area is expected to grow by 34% from 2005 to 2010. This increase in demand will be met by the construction of new reservoirs. However, reservoirs are dependent on rainfall and during prolonged periods of drought, as occurred in 1998, they could become empty. Therefore it is of great importance to develop alternative sources of water supply, including groundwater, to mitigate the effects of a serious water crisis. In this paper, results from a preliminary study on Kuala Lumpur's groundwater resources are presented. Modelling of the city's groundwater resources is extremely difficult given the limitations imposed by data availability and the karstic nature of some aquifers. Hence, the research presented here serves as a starting point for further studies rather than providing any definitive conclusions. In addition to the study results, the planning implications of groundwater extraction are discussed.

GROUNDWATER EXTRACTION MODELLING FOR KUALA LUMPUR WATER RESOURCE PLANNING

Portable water consumption in Kuala Lumpur and the surrounding area is expected to grow by 34% from 2005 to 2010. This increase in demand will be met by the construction of new reservoirs. However, reservoirs are dependent on rainfall and during prolonged periods of drought, as occurred in 1998, they could become empty. Therefore it is of great importance to develop alternative sources of water supply, including groundwater, to mitigate the effects of a serious water crisis. In this paper, results from a preliminary study on Kuala Lumpur's groundwater resources are presented. Modelling of the city's groundwater resources is extremely difficult given the limitations imposed by data availability and the karstic nature of some aquifers. Hence, the research presented here serves as a starting point for further studies rather than providing any definitive conclusions. In addition to the study results, the planning implications of groundwater extraction are discussed.

Sustainable Development in Northern Africa: The Argan Forest Case

The argan tree is a slow growing tree exclusively endemic in the dry lowlands of Southwest Morocco. The argan forest constitutes a long time ignored specific biotope that has been declared a Biosphere Reserve by UNESCO in 1998. The argan forest is particularly fragile to climate change. Forecasts show annual precipitation levels and prolonged drought periods that could severely threaten the future of the argan forest. In some places, the argan forest is already damaged, resulting in the retreat of the argan tree and the subsequent desert encroachment. An acceleration of this trend would have devastating consequences. In response, some twenty years ago, an ambitious, unique in Northern-Africa, and government-supported program was initiated in Morocco to rescue the argan tree via the sustainable development of the argan forest. Because in the late 1980s, sustainable development in developing countries was often considered as a utopia, the argan forest case represents a sign of progress, as it is also an interesting and unique experience in Africa. This review analyses the process followed, the measures taken, the pitfalls encountered, and the results obtained during the last two decades. It also points out the measures that still need to be taken before declaring the argan forest rescue mission is accomplished.

Avaliação da qualidade da água superficial dos cursos de água do município de Pelotas-RS, Brasil

The present work was performed in the municipality of Pelotas, RS, Brazil with the objective of evaluating water quality from the years of 1996 to 1998, in the principal waterways which pass through the municipality using the Water Quality Index of Bascaran (IQA b). It was verified that the water quality in the evaluated bodies was acceptable with the exception of the Eclusa and Santa Barbara reservoirs, in which phosphorus is the most important pollutant. During the period of prolonged drought from 1996 to 1997, there was a reduction in the IQA b. The index also reflected the environmental status verified in the region due to intensive agriculture and the release of a large portion of domestic and industrial wastes to the waterways without previous treatment.

Evaluation of surface water quality in waterways located in the municipality of Pelotas, RS, Brazil

The present work was performed in the municipality of Pelotas, RS, Brazil with the objective of evaluating water quality from the years of 1996 to 1998, in the principal waterways which pass through the municipality using the Water Quality Index of Bascaran (IQAb). It was verified that the water quality in the evaluated bodies was acceptable with the exception of the Eclusa and Santa Barbara reservoirs, in which phosphorus is the most important pollutant. During the period of prolonged drought from 1996 to 1997, there was a reduction in the IQAb. The index also reflected the environmental status verified in the region due to intensive agriculture and the release of a large portion of domestic and industrial wastes to the waterways without previous treatment.

Temporary fragmentation of a marginal lake and its effects on zooplankton community structure and organization

A river lateral lake (Coqueiral Lake marginal to Paranapanema River in its mouth zone into Jurumirim Reservoir, São Paulo, Brazil) presented fragmentation into four small isolated bodies of water during a prolonged drought period, disrupting the link with the river. The aim of this work was to compare the temporal modifications on zooplankton community structure (total abundance, species richness, and diversity) in the four water bodies. Zooplankton samplings and abiotic factor measurements were made in two periods--during isolation phase of the lake in relation to river and after re-establishment of hydrologic connectivity. A concentration effect on zooplankton abundance was recorded with drought progression, but without significant modifications in species richness and diversity. When the river inundation pulse occurred, a reduction in total zooplankton density was observed due to the dilution effect and a significant increase in species richness and diversity was recorded. Lateral water influx from the river to the lacustrine environment acts as a temporary disturbance factor on the zooplankton community structure. Zooplankton species composition presented some modifications between the two periods. Zooplankton organism drift in water from the river to the lake, removal of individuals from the aquatic macrophytes, and eclosion of resting eggs from sediment are probable factors that can increase zooplankton species richness immediately after lateral pulse inundation with water by the river.

A modelling study of the effects of land management and climatic variations on groundwater inflow to Lake St Lucia, South Africa

Over the past few years groundwater has been recognized as an important contributor of freshwater to Lake St Lucia, South Africa during periods of prolonged drought. This has led to a management strategy aiming at increasing the groundwater recharge and minimizing groundwater use through active manipulation of the vegetation. For the Eastern Shores on the edge of Lake St Lucia, the replacement of vast areas of pine (Pinus elliottii) plantations with grassland over the past decade, combined with a strict burning regime, has led to a general rise of the water table, which has increased the groundwater seepage to Lake St Lucia. A numerical groundwater model has been applied to assess the effects of local management strategies on the mass balance of a shallow aquifer and these are compared to the effects of predicted climate and sea-level change for this area. The simulations indicate that local management actions that are being applied to the Eastern Shores have positive effects on the groundwater flux into Lake St Lucia and that they outweigh potential negative effects of future climate and sea-level change predicted for this area.

Precipitation pulses enhance respiration of Mediterranean ecosystems: the balance between organic and inorganic components of increased soil CO2 efflux

AbstractIn regions characterized by arid seasons, such as the Mediterranean basin, soil moisture is a major driver of ecosystem CO2 efflux during periods of drought stress. Here, a rain event can induce a disproportional respiratory pulse, releasing an amount of CO2 to the atmosphere that may significantly contribute to the annual ecosystem carbon balance. The mechanisms behind this pulse are unclear, and it is still unknown whether it is due to the stimulation of autotrophic, heterotrophic and/or inorganic CO2 fluxes. On the Mediterranean island of Pianosa, eddy flux measurements showed respiratory pulses after rain events following prolonged drought periods, which occurred in the summer of 2003 and 2006. To investigate the mechanisms of this observed enhanced respiration fluxes and partition of the soil CO2 sources, two water manipulation experiments were performed. The first was designed to estimate the effect of soil rewetting on soil CO2 efflux, in the different ecosystem types existing on the island (i.e. woodland, ex‐agricultural and Mediterranean shrubland). The second was a soil CO2 partitioning experiment to investigate the relative contribution of inorganic and organic CO2 sources to soil respiration, under dry and wet soil conditions. Our results suggest that the pulse in the CO2 efflux is primarily due to the enhancement of heterotrophic respiration, likely caused by the degradation of easily decomposable substrates, accumulated in soils during the dry period. In fact, the vegetation at the site was senescent and did not play any significant role in CO2 exchange, as suggested by the absence of diurnal CO2 uptake in eddy covariance measurements. In addition, soil rewetting did not significantly enhance inorganic CO2 efflux.