Daniel G. Kingston

Uncertainty in the estimation of potential evapotranspiration under climate change

21st century climate change is projected to result in an intensification of the global hydrological cycle, but there is substantial uncertainty in how this will impact freshwater availability. A relatively overlooked aspect of this uncertainty pertains to how different methods of estimating potential evapotranspiration (PET) respond to changing climate. Here we investigate the global response of six different PET methods to a 2 degrees C rise in global mean temperature. All methods suggest an increase in PET associated with a warming climate. However, differences in PET climate change signal of over 100% are found between methods. Analysis of a precipitation/PET aridity index and regional water surplus indicates that for certain regions and GCMs, choice of PET method can actually determine the direction of projections of future water resources. As such, method dependence of the PET climate change signal is an important source of uncertainty in projections of future freshwater availability. Citation: Kingston, D. G., M. C. Todd, R. G. Taylor, J. R. Thompson, and N. W. Arnell (2009), Uncertainty in the estimation of potential evapotranspiration under climate change, Geophys. Res. Lett., 36, L20403, doi: 10.1029/2009GL040267.

Large-Scale Climatic Controls on New England River Flow

Abstract Understanding atmospheric drivers of river flow variability necessitates clear knowledge of the process chain linking climate and hydrology, yet the nature of such linkages remains poorly understood for the New England region of the northeastern United States. This research gap is addressed through a composite analysis of large-scale climatic controls on monthly high and low river flow in New England for 1958–2001, based on 40-yr ECMWF Re-Analysis (ERA-40) data. Analysis is focused on climate fields at the North Atlantic spatial scale, with particular attention given to the influence of the North Atlantic Oscillation (NAO). High (low) river flow is shown to be characterized by greater (lower) geopotential height throughout the year, and from December to April, higher (lower) temperature. Wind speed is inversely associated with river flow in all months, with wind direction more southerly (northerly) under high (low) flow situations. Relative vorticity differences reveal more cyclonic circulation c...

European-Scale Drought: Understanding Connections between Atmospheric Circulation and Meteorological Drought Indices

AbstractQuantification of large-scale climate drivers of drought is necessary to understand better and manage these spatially extensive and often prolonged natural hazards. Here, this issue is advanced at the continental scale for Europe. Drought events are identified using two indices—the 6-month cumulative standardized precipitation and standardized precipitation evapotranspiration indices (SPI-6 and SPEI-6, respectively)—both calculated using the gridded Water and Global Change (WATCH) Forcing Dataset for 1958–2001. Correlation of monthly time series of the percentage of European area in drought with geopotential height for 1958–2001 indicates that a weakening of the prevailing westerly circulation is associated with drought onset. Such conditions are linked to variations in the eastern Atlantic/western Russia (EA/WR) and North Atlantic Oscillation (NAO) atmospheric circulation patterns. Event-based analysis of the most widespread European droughts reveals that a higher number are identified by the SPE...

Climate change uncertainty in environmental flows for the Mekong River

Abstract A MIKE SHE model of the Mekong, calibrated and validated for 12 gauging stations, is used to simulate climate change scenarios associated with a 2°C increase in global mean temperature projected by seven general circulation models (GCMs). Impacts of each scenario on the river ecosystem and, hence, uncertainty associated with different GCMs are assessed through an environmental flow method based on the range of variability approach. Ecologically relevant hydrological indicators are evaluated for the baseline and each scenario. Baseline-to-scenario change is assessed against thresholds that define likely risk of ecological impact. They are aggregated into single scores for high and low flows. The results demonstrate considerable inter-GCM differences in risk of change. Uncertainty is larger for low flows, with some GCMs projecting high and medium risk at the majority of locations, and others suggesting widespread no or low risk. Inter-GCM differences occur along the main Mekong, as well as within major tributaries. Editor Z.W. Kundzewicz Citation Thompson, J.R., Laizé, C.L.R., Green, A.J., Acreman, M.C., and Kingston, D.G., 2014. Climate change uncertainty in environmental flows for the Mekong River. Hydrological Sciences Journal, 59 (3–4), 935–954.

Ocean–Atmosphere Forcing of Summer Streamflow Drought in Great Britain

AbstractDroughts are high-impact events that have substantial implications for both human and natural systems. As such, improved understanding of the hydroclimatological processes involved in drought development is a major scientific imperative of direct practical relevance. To address this research need, this paper investigates the chain of processes linking antecedent ocean–atmosphere variation to summer streamflow drought in Great Britain. Analyses are structured around four distinct drought regions (defined using hierarchical cluster analysis) for the period 1964–2001. Droughts were identified using a novel regional drought area index. Composite analysis of monthly sea surface temperature (SST) prior to drought onset reveals a horseshoe- or tripole-shaped pattern of North Atlantic SST anomalies that is similar to patterns of SST anomalies associated with the North Atlantic Oscillation (NAO). Patterns in geopotential height, wind, moisture vapor flux, and precipitation prior to drought onset support th...

Modelling water-level options for ecosystem services and assessment of climate change: Loktak Lake, northeast India

Abstract Water levels within Loktak Lake, an internationally important wetland, are regulated to prioritize hydropower over other ecosystem services. High water levels have impacted ecological conditions, in particular floating vegetated islands. Barrage operation options prioritizing hydropower, agriculture and the lake ecosystem are developed using a lake water balance model. Current hydropower abstractions can be maintained without ecologically damaging high water levels. Enhanced agricultural abstractions reduce levels to meet ecological requirements. The latter could be satisfied without compromising current hydropower and agricultural abstractions. An integrated option shows it is largely possible to balance hydropower and agricultural abstractions with wetland water-level requirements. Sustainability of barrage operation options is assessed under climate change scenarios. Higher monsoon precipitation and river flow can be accommodated. Larger dry-season drawdowns impact most barrage operation options, especially the integrated option. Results demonstrate the requirement to consider current and potential future climatic conditions when developing wetland water-level management plans. Editor D. Koutsoyiannis; Guest editor M.C. Acreman Citation Singh, C.R., Thompson, J.R., Kingston D.G. and French J.R., 2011. Modelling water-level options for ecosystem services and assessment of climate change, Loktak Lake, northeast India. Hydrological Sciences Journal 56 (8), 1518–1542.

GCM-related uncertainty for river flows and inundation under climate change: the Inner Niger Delta

ABSTRACT A semi-distributed hydrological model of the Niger River above and including the Inner Delta is developed. GCM-related uncertainty in climate change impacts are investigated using seven GCMs for a 2°C increase in global mean temperature, the hypothesised threshold of “dangerous” climate change. Declines in precipitation predominate, although some GCMs project increases for some sub-catchments, whilst PET increases for all scenarios. Inter-GCM uncertainty in projected precipitation is three to five times that of PET. With the exception of one GCM (HadGEM1), which projects a very small increase (3.9%), river inflows to the Delta decline. There is considerable uncertainty in the magnitude of these reductions, ranging from 0.8% (HadCM3) to 52.7% (IPSL). Whilst flood extent for HadGEM1 increases (mean annual peak +1405 km2/+10.2%), for other GCMs it declines. These declines range from almost negligible changes to a 7903 km2 (57.3%) reduction in the mean annual peak. Editor Z.W. Kundzewicz; Associate editor not assigned

Observed drought indices show increasing divergence across Europe

Recent severe European droughts raise the vital question: are we already experiencing measurable changes in drought likelihood that agree with climate change projections? The plethora of drought definitions compounds this question, requiring instead that we ask: how have various types of drought changed, how do these changes compare with climate projections, and what are the causes of observed differences? To our knowledge, this study is the first to reveal a regional divergence in drought likelihood as measured by the two most prominent meteorological drought indices: the Standardized Precipitation Index (SPI) and the Standardized Precipitation-Evapotranspiration Index (SPEI) across Europe over the period 1958–2014. This divergence is driven primarily by an increase in temperature from 1970–2014, which in turn increased reference evapotranspiration (ET0) and thereby drought area measured by the SPEI. For both indices, Europe-wide analysis shows increasing drought frequencies in southern Europe and decreasing frequencies in northern Europe. Notably, increases in temperature and ET0 have enhanced droughts in southern Europe while counteracting increased precipitation in northern Europe. This is consistent with projections under climate change, indicating that climate change impacts on European drought may already be observable and highlighting the potential for discrepancies among standardized drought indices in a non-stationary climate.

Determinants of vulnerability to the hydrological effects of climate change in rural communities: evidence from Nepal

The vulnerability of communities in the Himalayas to water stress caused by climate change depends on changes in the availability of water as well as how it is used. There has been little work done to reconcile these drivers of water stress in the Himalayas. This paper evaluates how climate change may affect water availability in two Nepalese mountain communities, Panglin and Tallo Lorpa, and assesses whether these changes drive vulnerability to water stress. First, estimates of hydrological change are made based on climate model output and hydroclimatological theory. Household surveys, focus group discussions and participatory rural appraisal techniques are used to assess vulnerability and adaptive capacity in each community. Finally, the expected effects of climate change on water availability are linked to findings on the communities’ vulnerability to these changes. The results show that both communities are vulnerable to changes in water availability under climate change, but this vulnerability is small in comparison to adaptation opportunities. However, the ability to appropriate benefits from these opportunities is constrained, and it is the extent of this inhibition that determines vulnerability. These findings demonstrate that Malthusian interpretations may be inappropriate in the Himalayas, and highlight the importance of the constraints to climate change adaptation.

Future river flows and flood extent in the Upper Niger and Inner Niger Delta: GCM-related uncertainty using the CMIP5 ensemble

ABSTRACT A semi-distributed hydrological model of the Upper Niger and the Inner Niger Delta is used to investigate the RCP 4.5 scenario for 41 CMIP5 GCMs in the 2050s and 2080s. In percentage terms, the range of change in precipitation is around four times as large as for potential evapotranspiration, which increases for most GCMs over most sub-catchments. Almost equal numbers of sub-catchment–GCM combinations experience positive and negative precipitation change. River discharge changes are equally uncertain. Inter-GCM range in mean discharge exceeds that of precipitation by three times in percentage terms. Declining seasonal flooding within the Inner Delta is dominant; 78 and 68% of GCMs project declines in October and November for the 2050s and 2080s, respectively. The 10- and 90-percentile changes in mean annual peak inundation range from −6136 km2 (−43%) to +987 km2 (+7%) for the 2050s and −6176 km2 (−43%) to +1165 km2 (+8.2%) for the 2080s.