Robert E. Nicholas

Invisible water, visible impact: groundwater use and Indian agriculture under climate change

India is one of the world’s largest food producers, making the sustainability of its agricultural system of global significance. Groundwater irrigation underpins India’s agriculture, currently boosting crop production by enough to feed 170 million people. Groundwater overexploitation has led to drastic declines in groundwater levels, threatening to push this vital resource out of reach for millions of small-scale farmers who are the backbone of India’s food security. Historically, losing access to groundwater has decreased agricultural production and increased poverty. We take a multidisciplinary approach to assess climate change challenges facing India’s agricultural system, and to assess the effectiveness of large-scale water infrastructure projects designed to meet these challenges. We find that even in areas that experience climate change induced precipitation increases, expansion of irrigated agriculture will require increasing amounts of unsustainable groundwater. The large proposed national river linking project has limited capacity to alleviate groundwater stress. Thus, without intervention, poverty and food insecurity in rural India is likely to worsen.

Drought Recurrence and Seasonal Rainfall Prediction in the Río Yaqui Basin, Mexico

Abstract A statistical approach is used to explore the variability of precipitation and meteorological drought in Mexico’s Rio Yaqui basin on seasonal-to-decadal time scales. For this purpose, a number of custom datasets have been developed, including a monthly 1900–2004 precipitation index for the Yaqui basin created by merging two gridded land surface precipitation products, a 349-yr tree-ring-based proxy for Yaqui wintertime rainfall, and a variety of large-scale climate indices derived from gridded SST records. Although significantly more rain falls during the summer (June–September) than during the winter (November–April), wintertime rainfall is over 3 times as variable relative to the climatological mean. Summertime rainfall appears to be unrelated to any large-scale patterns of variability, but a strong relationship between ENSO and Yaqui rainfall during the winter months offers the possibility of meaningful statistical prediction for this season’s precipitation. Analysis of both historical and rec...

Increasing temperature forcing reduces the Greenland Ice Sheet’s response time scale

Damages from sea level rise, as well as strategies to manage the associated risk, hinge critically on the time scale and eventual magnitude of sea level rise. Satellite observations and paleo-data suggest that the Greenland Ice Sheet (GIS) loses mass in response to increased temperatures, and may thus contribute substantially to sea level rise as anthropogenic climate change progresses. The time scale of GIS mass loss and sea level rise are deeply uncertain, and are often assumed to be constant. However, previous ice sheet modeling studies have shown that the time scale of GIS response likely decreases strongly with increasing temperature anomaly. Here, we map the relationship between temperature anomaly and the time scale of GIS response, by perturbing a calibrated, three-dimensional model of GIS behavior. Additional simulations with a profile, higher-order, ice sheet model yield time scales that are broadly consistent with those obtained using the three-dimensional model, and shed light on the feedbacks in the ice sheet system that cause the time scale shortening. Semi-empirical modeling studies that assume a constant time scale of sea level adjustment, and are calibrated to small preanthropogenic temperature and sea level changes, may underestimate future sea level rise. Our analysis suggests that the benefits of reducing greenhouse gas emissions, in terms of avoided sea level rise from the GIS, may be greatest if emissions reductions begin before large temperature increases have been realized. Reducing anthropogenic climate change may also allow more time for design and deployment of risk management strategies by slowing sea level contributions from the GIS.

Empirical Downscaling of High-Resolution Regional Precipitation from Large-Scale Reanalysis Fields

This study describes an EOF-based technique for statistical downscaling of high-spatial-resolution monthlymean precipitation from large-scale reanalysis circulationfields. The method is demonstrated and evaluated for fourwidelyseparatedlocations:thesoutheasternUnitedStates,theupperColoradoRiverbasin,China’sJiangxi Province,andcentralEurope.Foreachlocation,theEOF-baseddownscalingmodelssuccessfullyreproducethe observed annual cycle while eliminating the biases seen in NCEP‐NCAR reanalysis precipitation. They also frequently reproduce the monthly precipitation anomalies with greater fidelity than is seen in the precipitation field derived directly from reanalysis, and they outperform a suite of regional climate models over the two U.S. locations. With the relatively high skill achieved over a range of climate regimes, this technique may be a viable alternative to numerical downscaling of monthly-mean precipitation for many locations.

Projected impacts of climate change on habitat availability for an endangered parakeet

In tropical montane cloud forests, climate change can cause upslope shifts in the distribution ranges of species, leading to reductions in distributional range. Endemic species with small ranges are particularly vulnerable to such decreases in range size, as the population size may be reduced significantly. To ensure the survival of cloud forest species in the long term, it is crucial to quantify potential future shifts in their distribution ranges and the related changes in habitat availability in order to assure the long-term effectiveness of conservation measures. In this study, we assessed the influence of climate change on the availability of forested habitat for the endemic El Oro parakeet. We investigated the future range shift by modelling the climatic niche of the El Oro parakeets and projecting it to four different climate change scenarios. Depending on the intensity of climate change, the El Oro parakeets shift their range between 500 and 1700 m uphill by the year 2100. On average, the shift is accompanied by a reduction in range size to 15% and a reduction in forested habitat to only 10% of the original extent. Additionally, the connectivity between populations in different areas is decreasing in higher altitudes. To prevent a population decline due to habitat loss following an upslope range shift, it will be necessary to restore habitat across a large elevational span in order to allow for movement of El Oro parakeets into higher altitudes.

Statistics and the Future of the Antarctic Ice Sheet

37 One of the enduring symbols of the impact of climate change is that of a polar bear drifting in the sea, alone on its own piece of ice. For those who are left untouched by the loneliness of drifting polar bears, images of partially submerged lands and the devastation wrought by storm surges showcase some potentially frightening impacts of sea level rise on human life. The threat of sea level rise, in turn, is linked to the melting of ice sheets. Ice sheets are, therefore, important to understanding our planet, as well as learning about how our future may be affected by climate change. A promising approach to improving our understanding of ice sheets and derive sound projections of their future is to combine ice sheet physics, statistical modeling, and computing. First, what exactly is an ice sheet? It is an enormous mass of glacial land ice, more than 50,000 square kilometers in extent. The Antarctic ice sheet extends over 14 million square kilometers while the Greenland ice sheet extends over 1.7 million square kilometers. To put this in perspective, the area covered by the Antarctic ice sheet is comparable to the continental United States and Mexico combined. In fact, the Greenland and Antarctic ice sheets contain more than 99% of the freshwater ice in the world. Roughly speaking, melting the entire Greenland ice sheet would result in sea level rise of around 7 meters (23 feet) while if the entire Antarctic ice sheet melted, it would result in sea level rise of around 57 meters (187 feet). Statistics and the Future of the Antarctic Ice Sheet