Hammond Hill Research Catchment: Supporting Hydrologic Investigations of Rooting Zone and Vegetation Water Dynamics under Climate Change

Abstract. Drylands cover about 40% of the terrestrial land surface and account for approximately 40% of global net primary productivity. Water is fundamental to the biophysical processes that sustain ecosystem function and food production, particularly in drylands where a tight coupling exists between ecosystem productivity, surface energy balance, biogeochemical cycles, and water resource availability. Currently, drylands support at least 2 billion people and comprise both natural and managed ecosystems. In this synthesis, we identify some current critical issues in the understanding of dryland systems and discuss how arid and semiarid environments are responding to the changes in climate and land use. The issues range from societal aspects such as rapid population growth, the resulting food and water security, and development issues, to natural aspects such as ecohydrological consequences of bush encroachment and the causes of desertification. To improve current understanding and inform upon the needed research efforts to address these critical issues, we identify some recent technical advances in terms of monitoring dryland water dynamics, water budget and vegetation water use, with a focus on the use of stable isotopes and remote sensing. These technological advances provide new tools that assist in addressing critical issues in dryland ecohydrology under climate change.

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The influence of vegetation water dynamics on the ASCAT backscatter-incidence angle relationship in the Amazon

10.5194/hess-2021-406 ◽

2021 ◽

Author(s):

Ashwini Petchiappan ◽

Susan C. Steele-Dunne ◽

Mariette Vreugdenhil ◽

Sebastian Hahn ◽

Wolfgang Wagner ◽

...

Keyword(s):

Seasonal Cycle ◽

Incidence Angle ◽

Water Dynamics ◽

Plant Water ◽

Vegetation Monitoring ◽

Equivalent Water Thickness ◽

Moisture Availability ◽

Phenological Changes ◽

Data Record ◽

Vegetation Water

Abstract. Microwave observations are sensitive to plant water content and could therefore provide essential information on biomass and plant water status in ecological and agricultural applications. The combined data record of the C-band scatterometers on ERS 1/2, the Metop series and the planned Metop Second Generation satellites will span over 40 years, which would provide a long-term perspective on the role of vegetation in the climate system. Recent research has indicated that the unique viewing geometry of ASCAT could be exploited to observe vegetation water dynamics. The incidence angle dependence of backscatter can be described with a second order polynomial, the slope and curvature of which are related to vegetation. In a study limited to grasslands, seasonal cycles, spatial patterns and interannual variability in the slope and curvature were found to vary among grassland types and were attributed to differences in moisture availability, growing season length and phenological changes. To exploit ASCAT slope and curvature for global vegetation monitoring, their dynamics over a wider range of vegetation types needs to be quantified and explained in terms of vegetation water dynamics. Here, we compare ASCAT data with meteorological data and GRACE Equivalent Water Thickness (EWT) to explain the dynamics of ASCAT backscatter, slope and curvature in terms of moisture availability and demand. We consider differences in the seasonal cycle, diurnal differences, and the response to the 2010 and 2015 droughts across ecoregions in the Amazon basin and surroundings. Results show that spatial and temporal patterns in backscatter reflect moisture availability indicated by GRACE EWT. Slope and curvature dynamics vary considerably among the ecoregions. The evergreen forests, often used as a calibration target, exhibit very stable behaviour even under drought conditions. The limited seasonal variation follows changes in the radiation cycle, and may indicate phenological changes such as litterfall. In contrast, the diversity of land cover types within the Cerrado region results in considerable heterogeneity in terms of the seasonal cycle and the influence of drought on both slope and curvature. Seasonal flooding in forest and savanna areas also produced a distinctive signature in terms of the backscatter as a function of incidence angle. This improved understanding of the incidence angle behaviour of backscatter increases our ability to interpret and make optimal use of the ASCAT data record and VOD products for vegetation monitoring.

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Drought-influenced mortality of tree species with different predawn leaf water dynamics in a decade-long study of a central US forest

Biogeosciences ◽

10.5194/bg-12-2831-2015 ◽

2015 ◽

Vol 12 (10) ◽

pp. 2831-2845 ◽

Cited By ~ 30

Author(s):

L. Gu ◽

S. G. Pallardy ◽

K. P. Hosman ◽

Y. Sun

Keyword(s):

Water Potential ◽

Tree Species ◽

Tree Mortality ◽

Leaf Water ◽

Water Dynamics ◽

Annual Variations ◽

Rooting Zone ◽

Risk Of Death ◽

Drought Tolerant ◽

Precipitation Regimes

Abstract. Using decade-long continuous observations of tree mortality and predawn leaf water potential (ψpd) at the Missouri Ozark AmeriFlux (MOFLUX) site, we studied how the mortality of important tree species varied and how such variations may be predicted. Water stress determined inter-annual variations in tree mortality with a time delay of 1 year or more, which was correlated fairly tightly with a number of quantitative predictors formulated based on ψpd and precipitation regimes. Predictors based on temperature and vapor pressure deficit anomalies worked reasonably well, particularly for moderate droughts. The exceptional drought of the year 2012 drastically increased the mortality of all species, including drought-tolerant oaks, in the subsequent year. The drought-influenced tree mortality was related to the species position along the spectrum of ψpd regulation capacity with those in either ends of the spectrum being associated with elevated risk of death. Regardless of species and drought intensity, the ψpd of all species recovered rapidly after sufficiently intense rain events in all droughts. This result, together with a lack of immediate leaf and branch desiccation, suggests an absence of catastrophic hydraulic disconnection in the xylem and that tree death was caused by significant but indirect effects. Species differences in the capacity of regulating ψpd and its temporal integral were magnified under moderate drought intensities but diminished towards wet and dry extremes. Severe droughts may overwhelm the capacity of even drought-tolerant species to maintain differential levels of water potential as the soil becomes exhausted of available water in the rooting zone, thus rendering them more susceptible to death if predisposed by other factors such as age.

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Adapting water allocation management to drought scenarios

Natural Hazards and Earth System Science ◽

10.5194/nhess-8-293-2008 ◽

2008 ◽

Vol 8 (2) ◽

pp. 293-302 ◽

Cited By ~ 7

Author(s):

P. Giacomelli ◽

A. Rossetti ◽

M. Brambilla

Keyword(s):

Climate Change ◽

Water Resources ◽

Regional Scale ◽

Water Dynamics ◽

Climate Change Scenarios ◽

Watershed Scale ◽

Summer Period ◽

Water Management System ◽

Hydroelectric Reservoirs ◽

Change Dynamics

Abstract. Climate change dynamics have significant consequences on water resources on a watershed scale. With water becoming scarcer and susceptible to variation, the planning and reallocation decisions in watershed management need to be reviewed. This research focuses on an in-depth understanding of the current allocation balance of water resources among competitors, placed along the course of the Adda River. In particular, during the summer period, the demand for water dramatically increases. This is due to the increase in irrigation activities in the lower part of the basin and to the highest peaks of tourist inflow, in the Como Lake and Valtellina areas. Moreover, during these months, the hydroelectric reservoirs in the upper part of the Adda River basin (the Valtellina) retain most of the volume of water coming from the snow and glacier melt. The existing allocation problem among these different competing users is exacerbated by the decreasing water supplies. The summer of 2003 testified the rise in a number of allocation problems and situations of water scarcity that brought about environmental and economical consequences. The RICLIC project is committed to the understanding of water dynamics on a regional scale, to quantify the volumes involved and offer local communities an instrument to improve a sustainable water management system, within uncertain climate change scenarios.

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Reconstructing Continuous Vegetation Water Content To Understand Sub-daily Backscatter Variations

10.5194/hess-2021-459 ◽

2021 ◽

Author(s):

Paul C. Vermunt ◽

Susan C. Steele-Dunne ◽

Saeed Khabbazan ◽

Jasmeet Judge ◽

Nick C. van de Giesen

Keyword(s):

Soil Moisture ◽

Water Content ◽

Water Cycle ◽

Water Dynamics ◽

High Temporal Resolution ◽

Daily Variations ◽

Vegetation Water Content ◽

Dew Formation ◽

Vegetation Water ◽

Canopy Water

Abstract. Microwave observations are sensitive to vegetation water content (VWC). Consequently, the increasing temporal and spatial resolution of spaceborne microwave observations creates a unique opportunity to study vegetation water dynamics and its role in the diurnal water cycle. However, we currently have a limited understanding of sub-daily variations in VWC and how they affect passive and active microwave observations. This is partly due to the challenges associated with measuring internal VWC for validation, particularly non-destructively and at timescales of less than a day. In this study, we aimed to (1) use field sensors to reconstruct diurnal and continuous records of internal VWC of corn, and (2) use these records to interpret the sub-daily behaviour of a 10-day time series of polarimetric L-band backscatter with high temporal resolution. Sub-daily variations of internal VWC were calculated based on the cumulative difference between estimated transpiration and sap flow rates at the base of the stems. Destructive samples were used to constrain the estimates and for validation. The inclusion of continuous surface canopy water estimates (dew or interception) and surface soil moisture allowed us to attribute hour-to-hour backscatter dynamics to either internal VWC, surface canopy water or soil moisture variations. Our results showed that internal VWC varied with 10–20 % during the day in non-stressed conditions, and the effect on backscatter was significant. Diurnal variations of internal VWC and nocturnal dew formation affected vertically polarized backscatter most. Moreover, on a typical dry day, backscatter variations were 1.5 (HH-pol) to 3 (VV-pol) times more sensitive to VWC than to soil moisture. These results demonstrate that radar observations have the potential to provide unprecedented insight into the role of vegetation water dynamics in land-atmosphere interactions at sub-daily timescales.

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LONG-TERM MONITORING OF WATER DYNAMICS IN THE SAHEL REGION USING THE MULTI-SAR-SYSTEM

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xli-b8-313-2016 ◽

2016 ◽

Vol XLI-B8 ◽

pp. 313-320 ◽

Cited By ~ 1

Author(s):

A. Bertram ◽

A. Wendleder ◽

A. Schmitt ◽

M. Huber

Keyword(s):

Climate Change ◽

Human Population ◽

Dynamic Change ◽

Open Water ◽

Water Dynamics ◽

Long Term Monitoring ◽

Sar Data ◽

Sahel Region ◽

Term Monitoring

Fresh water is a scarce resource in the West-African Sahel region, seasonally influenced by droughts and floods. Particularly in terms of climate change, the importance of wetlands increases for flora, fauna, human population, agriculture, livestock and fishery. Hence, access to open water is a key factor. Long-term monitoring of water dynamics is of great importance, especially with regard to the spatio-temporal extend of wetlands and drylands. It can predict future trends and facilitate the development of adequate management strategies. Lake Tabalak, a Ramsar wetland of international importance, is one of the most significant ponds in Niger and a refuge for waterbirds. Nevertheless, human population growth increased the pressure on this ecosystem, which is now degrading for all uses. The main objective of the study is a long-term monitoring of the Lake Tabalak’s water dynamics to delineate permanent and seasonal water bodies, using weather- and daytime-independent multi-sensor and multi-temporal Synthetic Aperture Radar (SAR) data available for the study area. Data of the following sensors from 1993 until 2016 are used: Sentinel-1A, TerraSARX, ALOS PALSAR-1/2, Envisat ASAR, RADARSAT-1/2, and ERS-1/2. All SAR data are processed with the Multi-SAR-System, unifying the different characteristics of all above mentioned sensors in terms of geometric, radiometric and polarimetric resolution to a consistent format. The polarimetric representation in Kennaugh elements allows fusing single-polarized data acquired by older sensors with multi-polarized data acquired by current sensors. The TANH-normalization guarantees a consistent and therefore comparable description in a closed data range in terms of radiometry. The geometric aspect is solved by projecting all images to an earth-fixed coordinate system correcting the brightness by the help of the incidence angle. The elevation model used in the geocoding step is the novel global model produced by the TanDEM-X satellite mission. The advantage of the Multi-SAR-System is that it comprises ortho-rectification, radiometric enhancement, normalization and Kennaugh decomposition, independent from sensors, modes, polarizations or acquisition date of SAR data. In addition, optical satellite data can be included as well, to fill gaps where SAR data are missing due to the special normalization scheme. This kind of pre-processing is exclusively implemented at the Earth Observation Center of the German Aerospace Center in Oberpfaffenhofen, Germany. Therefore, the dynamic change of the open water of the Lake Tabalak could be classified over dry and rainy seasons and years, using different SAR data. The study provides a unique database and contributes to a better understanding of wetland systems in the Sahel region influenced by human pressure and climate change.

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Spatial and Temporal Changes in Surface Water Area of Sri Lanka over a 30-Year Period

Remote Sensing ◽

10.3390/rs12223701 ◽

2020 ◽

Vol 12 (22) ◽

pp. 3701

Author(s):

Deepakrishna Somasundaram ◽

Fangfang Zhang ◽

Sisira Ediriweera ◽

Shenglei Wang ◽

Junsheng Li ◽

...

Keyword(s):

Climate Change ◽

Surface Water ◽

Sri Lanka ◽

Anthropogenic Activities ◽

Water Area ◽

Temporal Changes ◽

Water Bodies ◽

Water Dynamics ◽

Annual Growth Rate ◽

Spatial And Temporal Changes

Sri Lanka contains a large number of natural and man-made water bodies, which play an essential role in irrigation and domestic use. The island has recently been identified as a global hotspot of climate change extremes. However, the extent, spatial distribution, and the impact of climate and anthropogenic activities on these water bodies have remained unknown. We investigated the distribution, spatial and temporal changes, and the impacts of climatic and anthropogenic drivers on water dynamics in Dry, Intermediate, and Wet zones of the island. We used Landsat 5 and Landsat 8 images to generate per-pixel seasonal and annual water occurrence frequency maps for the period of 1988–2019. The results of the study demonstrated high inter- and intra-annual variations in water with a rapid increase. Further, results showed strong zonal differences in water dynamics, with most dramatic variations in the Dry zone. Our results revealed that 1607.73 km2 of the land area of the island is covered by water bodies, among this 882.01 km2 (54.86%) is permanent and 725.72 km2 (45.14%) is seasonal water area. Total inland seasonal water increased with a dramatic annual growth rate of 7.06 ± 1.97 km2 compared to that of permanent water (4.47 ± 2.08 km2/year). Sri Lanka has the highest permanent water area during December–February (1045.97 km2), and drops to the lowest in May–September (761.92 km2) when the seasonal water (846.46 km2) is higher than permanent water. The surface water area was positively related to both precipitation and Gross Domestic Product, while negatively related to the temperature. Findings of our study provide important insights into possible spatiotemporal changes in surface water availability in Sri Lanka under certain climate change and anthropogenic activities.

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Warming reduces the growth and diversity of biological soil crusts in a semi-arid environment: implications for ecosystem structure and functioning

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2011.0344 ◽

2012 ◽

Vol 367 (1606) ◽

pp. 3087-3099 ◽

Cited By ~ 77

Author(s):

Cristina Escolar ◽

Isabel Martínez ◽

Matthew A. Bowker ◽

Fernando T. Maestre

Keyword(s):

Climate Change ◽

Soil Stabilization ◽

Arid Environment ◽

Biological Soil Crusts ◽

Water Dynamics ◽

Annual Rainfall ◽

Ecosystem Structure ◽

Positive Effects ◽

Soil Crusts ◽

Semi Arid

Biological soil crusts (BSCs) are key biotic components of dryland ecosystems worldwide that control many functional processes, including carbon and nitrogen cycling, soil stabilization and infiltration. Regardless of their ecological importance and prevalence in drylands, very few studies have explicitly evaluated how climate change will affect the structure and composition of BSCs, and the functioning of their constituents. Using a manipulative experiment conducted over 3 years in a semi-arid site from central Spain, we evaluated how the composition, structure and performance of lichen-dominated BSCs respond to a 2.4°C increase in temperature, and to an approximately 30 per cent reduction of total annual rainfall. In areas with well-developed BSCs, warming promoted a significant decrease in the richness and diversity of the whole BSC community. This was accompanied by important compositional changes, as the cover of lichens suffered a substantial decrease with warming (from 70 to 40% on average), while that of mosses increased slightly (from 0.3 to 7% on average). The physiological performance of the BSC community, evaluated using chlorophyll fluorescence, increased with warming during the first year of the experiment, but did not respond to rainfall reduction. Our results indicate that ongoing climate change will strongly affect the diversity and composition of BSC communities, as well as their recovery after disturbances. The expected changes in richness and composition under warming could reduce or even reverse the positive effects of BSCs on important soil processes. Thus, these changes are likely to promote an overall reduction in ecosystem processes that sustain and control nutrient cycling, soil stabilization and water dynamics.

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Combined impact of local climate and soil properties on soil moisture patterns

10.5194/hess-2017-357 ◽

2017 ◽

Cited By ~ 1

Author(s):

Thushara Gunda ◽

Udeni P. Nawagamuwa ◽

George M. Hornberger

Keyword(s):

Climate Change ◽

Soil Moisture ◽

Soil Properties ◽

Temporal Variations ◽

Intermediate Zone ◽

Water Dynamics ◽

Climate Change Scenarios ◽

Local Climate ◽

Dry Zone ◽

Wet Zone

Abstract. Soil plays a key role in terrestrial water dynamics by retaining precipitation on land. A water balance approach is used to evaluate spatial and temporal variations in soil moisture in Sri Lanka, a country characterized by high spatial variability as reflected in the recognition of three regions of the country, the wet zone, the intermediate zone, and the dry zone. We show that a combination of local climate and soil properties drive spatial patterns of soil moisture deficits on the island, with soils buffering climate variability in the wet zone and enhancing drought patterns in the dry zone. Changes in historical temporal patterns are most notable for the intermediate zone, a region characterized by consistently variable deficits. Counterfactuals of climate change scenarios indicate temperature will drive increases in deficit likelihoods (up to 20 %) in the future, with greatest impact in the intermediate and dry zones, where more than 80 % of the national rice production is concentrated. Given that temperature projections are less uncertain than other climate change impacts, further evaluation of future water stresses are needed. Coupled with remotely-sensed soil moisture data, the findings from this study have implications for infrastructural planning and seasonal crop water allocations in zones with a degree of variability (i.e., neither consistently wet nor consistently dry). Because soil hydrologic regimes reflect inherent, local vulnerabilities, water management decisions need to incorporate regional variabilities in soil moisture dynamics in assessments of climate change adaptations.

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