This paper explores the use of active and passive microwave satellite soil moisture products for improving streamflow prediction within four large (>5000km2) semiarid catchments in Australia. We use ...the probability distributed model (PDM) under a data‐scarce scenario and aim at correcting two key controlling factors in the streamflow generation: the rainfall forcing data and the catchment wetness condition. The soil moisture analysis rainfall tool (SMART) is used to correct a near real‐time satellite rainfall product (forcing correction scheme) and an ensemble Kalman filter is used to correct the PDM soil moisture state (state correction scheme). These two schemes are combined in a dual correction scheme and we assess the relative improvements of each. Our results demonstrate that the quality of the satellite rainfall product is improved by SMART during moderate‐to‐high daily rainfall events, which in turn leads to improved streamflow prediction during high flows. When employed individually, the soil moisture state correction scheme generally outperforms the rainfall correction scheme, especially for low flows. Overall, the combined dual correction scheme further improves the streamflow predictions (reduction in root mean square error and false alarm ratio, and increase in correlation coefficient and Nash‐Sutcliffe efficiency). Our results provide new evidence of the value of satellite soil moisture observations within data‐scarce regions. We also identify a number of challenges and limitations within the schemes.
Key Points:
The state correction scheme leads to improved streamflow predictions, especially for low flows
The forcing correction scheme leads to improved rainfall estimates, which in turn leads to improved streamflow predictions
The combined dual correction scheme outperforms the individual schemes
Fjord sediments are increasingly recognized as high‐resolution archives of past hydrological and climate variability. Using them as such, however, requires a comprehensive understanding of the ...variables that affect their accumulation rates and properties. Here, we conduct a spatial and temporal study of sediment samples collected at the head of Martínez Channel (Chilean Patagonia, 48°S), to understand how the fjord's sediments register changes in the hydrology of Baker River, Chile's largest river in terms of mean annual discharge. We apply end‐member modeling to particle‐size distributions of: (a) river suspended sediments, (b) surface sediments collected along a proximal‐distal transect at the fjord head, and (c) fjord sediments collected in a sequential sediment trap at 15‐day resolution during two consecutive years. We then validate the use of the grain‐size end members for hydrological and climate reconstructions, using a sediment core that covers the last 35 years. Results show that the river suspended sediments and fjord sediments are consistently composed of two grain‐size subpopulations. The finest end member (EM1; mode 4.03 μm) reflects the meltwater contribution, which dominates in all but the winter season. The coarser end member (EM2; mode 18.7 μm) dominates in winter, when meltwater contribution is reduced, and is associated with rainfall. We show that the fluxes of EM1 and EM2 provide quantitative estimates of baseflow (r = 0.87, p < 0.001) and quickflow (r = 0.86, p < 0.001), respectively. Additionally, we propose that log (EM1/EM2) can be used to reconstruct meltwater production (r = 0.67, p < 0.001) and temperature (r = 0.81, p < 0.001) in the lower Baker River watershed. These results support the use of fjord sediments for quantitative reconstructions of hydrological and climate variability in partially glacierized watersheds.
Plain Language Summary
Sediments transported by rivers and deposited in fjords retain information about river discharge conditions and about the climate that prevails in the fjord watersheds. Fjord sediments are therefore frequently used to reconstruct past river discharge and climate conditions. Here, we show that the sediments deposited in the fjord in which Chile's largest river discharges are composed of a mixture of two grain size populations: fine particles originating from the melting of snow and glaciers, particularly in summer, and coarser particles representing sediments eroded during rainfall events. Our results reveal that the amount of fine particles deposited each day in the fjord represents the amount of water that melts from snow and glaciers. Similarly, the amount of coarse particles deposited in the fjord each day reflects the rain that fell in the watershed. To reconstruct changes in water originating from the melting of snow and glaciers in the past, we suggest measuring grain size on fjord sediment cores and using the ratio between the amount of fine and coarse particles. Since the melting of snow and glaciers depends on temperature, this ratio can also be used to reconstruct past changes in air temperature.
Key Points
The grain size of fjord sediments deposited at the head of Martínez Channel reflects Baker River discharge
Fluxes of the coarse and fine end members represent rainfall‐driven discharge and meltwater production, respectively
Temporal variations in the proportions of the grain‐size end members can be used to reconstruct meltwater production and temperature
Over the past 40 years, south-central Chile has experienced important land-use-induced land cover changes, with massive conversion from native forests (NF) to Pinus radiata D.Don and Eucalyptus spp. ...exotic forest plantations (FP). Several case studies have related this conversion to a reduction in water supply within small catchments (<100 ha). In this work, we explore the impacts of NF and FP on streamflow by using a large-sample catchment dataset recently developed for Chile. We select 25 large forested catchments (>20,000 ha) in south-central Chile (35° S–41° S), analyze their land cover and precipitation spatial distributions, and fit a regression model to quantify the influence of NF, FP, grassland (GRA) and shrubland (SHR) partitions on annual runoff. To assess potential effects of land cover changes on water supply, we use the fitted model (R2 = 0.84) in synthetic experiments where NF, GRA and SHR covers within the catchments are replaced by patches of FP. We show that annual runoff consistently decreases with increments of FP, although the magnitude of the change (ranging from 2.2% to 7.2% mean annual runoff decrease for 10,000 ha increment in FP) depends on several factors, including the initial land cover partition within the basin, the replaced land cover class, the area of the catchment, and the type of catchment (drier or humid). Finally, in the context of the mitigation strategies pledged in the Chilean NDC (Nationally Determined Contributions defined after the Paris Agreement), which include the afforestation of 100,000 ha (mainly native forest) by 2030, we quantify the impacts on water supply due to the afforestation of 100,000 ha with different combinations of NF and FP. We show that annual runoff is highly sensitive to the relative area of FP to NF: ratios of FP to NF areas of 10%, 50% and 90% would lead to 3%, −18% and −40% changes in mean annual runoff, respectively. Our results can be used in the discussion of public policies and decision-making involving forests and land cover changes, as they provide scientifically-based tools to quantify expected impacts on water resources. In particular, this knowledge is relevant for decision making regarding mitigation strategies pledged in the Chilean NDC.
Since 1981, water allocation in Chile has been based on a water use rights (WURs) market, with limited regulatory and supervisory mechanisms. The volume to be granted as permanent and eventual WURs ...is calculated from streamflow records, if stream gauge data are available, or from hydrologic parameter transfer from gauged to ungauged catchments, usually with less than 50 years of record. To test the performance of this allocation system, while analyzing the long-term natural variability in water resources, we investigated a 400 year-long (1590–2015) tree-ring reconstruction of runoff and historical water rights for Perquilauquén at Quella catchment, a tributary to the Maule River in Central Chile (35°S–36°30S). Furthermore, we assess how the current legislation would perform under a projected climate scenario, based on historical climate simulations of runoff calibrated against observed data, and future projections. Our analyses indicate that the allocation methodology currently applied by the Water Authority in Chile is very sensitive to the time window of data used, which leads to an underestimation of variability and long-term trends. According to the WURs database provided by the Chilean Water Directorate, WURs at Perquilauquén at Quella are already over-allocated. Considering regional climate projections, this condition will be exacerbated in the future. Furthermore, serious problems regarding the access and quality of information on already-granted WURs and actual water usage have been diagnosed, which further encumber environmental strategies to deal with and adapt to climate change. We emphasize the urgent need for a review and revision of current water allocation methodologies and water law in Chile, which are not concordant with the dynamics and non-stationarity of hydrological processes. Water scarcity and water governance are two of the key issues to be faced by Chile in the Anthropocene.
Since 2010, Chile has experienced one of the most severe droughts over the last century, the so-called mega-drought (MD). The MD conditions, combined with intensive agricultural activities and the ...current water management system, have led to water scarcity problems in Mediterranean and Semi-arid regions of Chile. An emblematic case is the Petorca basin, where a water crisis is undergone. To characterize this crisis, we analyzed water provision by using tree-ring records, remote sensing, instrumental data, and allocated water rights within the basin. Results indicate that the MD is the most severe dry period over the last 700-years of streamflow reconstruction. During the MD, streamflow and water bodies of the upper parts of the basin have been less affected than mid and low areas of this valley, where consumptive withdrawals reach up to 18% of the mean annual precipitation. This extracted volume is similar to the MD mean annual precipitation deficits. The impacts of the current drought, along with the drier climate projections for Central Chile, emphasize the urgency for faster policy changes related to water provision. Climate change adaptation plans and policies should enhance the current monitoring network and the public control of water use to secure the water access for inhabitants and productive activities.
Water allocation under climate change Barría Pilar; Sandoval, Ignacio Barría; Guzman, Carlos ...
Elementa (Washington, D.C.),
05/2021, Letnik:
9, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Chile is positioned in the 20th rank of water availability per capita. Nonetheless, water security levels vary across the territory. Around 70% of the national population lives in arid and semiarid ...regions, where a persistent drought has been experienced over the last decade. This has led to water security problems including water shortages. The water allocation and trading system in Chile is based on a water use rights (WURs) market, with limited regulatory and supervisory mechanisms, where the volume to be granted as permanent and eventual WURs is calculated from statistical analyses of historical streamflow records if available, or from empirical estimations if they are not. This computation of WURs does not consider the nonstationarity of hydrological processes nor climatic projections. This study presents the first large sample diagnosis of water allocation system in Chile under climate change scenarios. This is based on novel anthropic intervention indices (IAI), which were computed as the ratio between the total granted water volume to the water availability within 87 basins in north-central and southern Chile (30°S–42°S). The IAI were evaluated for the historical period (1979–2019) and under modeled-based climatic projections (2055–2080). According to these IAI levels, to date, there are 20 out of 87 overallocated basins, which under the assumption that no further WURs will be granted in the future, increases up to 25 basins for the 2055–2080 period. The results show that, to date most of north-central Chilean catchments already have a large anthropic intervention degree, and the increases for the future period occurs mostly in the southern region of the country (approximately 38°S), which has been considered as possible source of water for large water transfer projects (i.e., water roads). These indices and diagnosis are proposed as a tool to help policy makers to address water scarcity under climate change.
We introduce a set of global high-resolution (0.05°) precipitation (P) climatologies corrected for bias using streamflow (Q) observations from 9372 stations worldwide. For each station, we inferred ...the “true” long-term P using a Budyko curve, which is an empirical equation relating long-term P, Q, and potential evaporation. We subsequently calculated long-term bias correction factors for three state-of-the-art P climatologies the “WorldClim version 2” database (WorldClim V2); Climatologies at High Resolution for the Earth’s Land Surface Areas, version 1.2 (CHELSA V1.2 ); and Climate Hazards Group Precipitation Climatology, version 1 (CHPclim V1), after which we used random-forest regression to produce global gap-free bias correction maps for the P climatologies. Monthly climatological bias correction factors were calculated by disaggregating the long-term bias correction factors on the basis of gauge catch efficiencies. We found that all three climatologies systematically underestimate P over parts of all major mountain ranges globally, despite the explicit consideration of orography in the production of each climatology. In addition, all climatologies underestimate P at latitudes >60°N, likely because of gauge undercatch. Exceptionally high long-term correction factors (>1.5) were obtained for all three P climatologies in Alaska, High Mountain Asia, and Chile—regions characterized by marked elevation gradients, sparse gauge networks, and significant snowfall. Using the bias-corrected WorldClim V2, we demonstrated that other widely used P datasets (GPCC V2015, GPCP V2.3, and MERRA-2) severely underestimate P over Chile, the Himalayas, and along the Pacific coast of North America. Mean P for the global land surface based on the bias-corrected WorldClim V2 is 862 mm yr−1 (a 9.4% increase over the original WorldClim V2). The annual and monthly bias-corrected P climatologies have been released as the Precipitation Bias Correction (PBCOR) dataset, which is available online (http://www.gloh2o.org/pbcor/).
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