Asher Siebert | Columbia University (original) (raw)

Papers by Asher Siebert

100th American Meteorological Society Annual Meeting, Jan 13, 2020

Aspects of forecast skill in predicting seasonal characteristics using global climate models (GCM... more Aspects of forecast skill in predicting seasonal characteristics using global climate models (GCMs) are assessed over South Africa. The GCMs output is configured to predict number of rainfall days at South African Weather Service stations exceeding pre-defined threshold values for the austral summer seasons and to predict the rainfall totals of the onset months of the rainy seasons for eight homogeneous rainfall regions of South Africa. Using canonical correlation analysis (CCA) as statistical downscaling technique through model output statistics, the forecast skill levels of coupled ocean-atmosphere and uncoupled atmospheric models are determined through retroactively generated hindcasts. Both downscaled models have skill in predicting low and high number of rainfall days exceeding pre-defined thresholds for the austral summer seasons as well as rainfall totals of onset months. In addition to the forecast verification results, CCA pattern is performed to determine the dominating atmospheric circulation systems predicted to be controlling rainfall variations for the seasons and months of interest. CCA patterns for both the GCMs indicate that usually when there are anomalously negative (positive) predicted 850 hPa geopotential heights over South Africa, there are anomalously wet (dry) conditions over most parts of South Africa. The work has paved the way for the operational production of seasonal rainfall characteristics over South Africa in real time.

98th American Meteorological Society Annual Meeting, Jan 10, 2018

Journal of Applied Meteorology and Climatology, Mar 1, 2011

A statistical simulation framework is developed to explore the future frequencies of threshold-cr... more A statistical simulation framework is developed to explore the future frequencies of threshold-crossing events, focusing here on low seasonal rainfall totals. Global change (GC) is represented by a trend on the seasonal mean rainfall total. Natural decadal to multidecadal variability (MDV) is represented by an autoregressive process. Interannual variability (IV) of seasonal totals is represented by white noise with either a normal or skew normal distribution consistent with parameters observed in the historical record at the location being modeled. Monte Carlo simulations are undertaken for various combinations of the above components, and the authors evaluate the extent to which future event frequencies can be estimated from the statistics of previous years. The sample of four study locations used to illustrate the approach is drawn from the Millennium Villages Project in Africa, where the potential of index insurance as a development and adaptation tool has been considered, thereby bringing a targeted problem setting to the analyses. The simulations highlight a number of general principles. For example, it is shown that a 10% change in the mean rainfall can lead to a change of order times 2 in the number of threshold-crossing low seasonal rainfall totals, even without invoking any change in the characteristics of the IV. The magnitudes of change are also shown to be sensitive to the threshold studied, as well as to site-specific climate features (here, coefficient of variation and skewness). The framework developed permits quantification of how, especially in the near term (of order 30 years), MDV can strongly add to uncertainty about future event frequencies. Therefore, statistical treatment of estimated MDV magnitudes will often be a key input to optimal risk management, with further enhancements expected through explicit MDV forecasts. The results highlight the importance of finding optimal ways to update climate statistics such as event thresholds, in the presence of GC and MDV.

African Geographical Review, Nov 12, 2013

Weather, Climate, and Society, Jun 23, 2016

Index insurance has been viewed as a financial adaptation to climate risks with the potential for... more Index insurance has been viewed as a financial adaptation to climate risks with the potential for widespread application, especially in a developing world context. The potential for index insurance is explored in the context of hypothetical drought and flood contracts at the national level for farmers in the West African Sahel nations of Niger, Burkina Faso, and Mali. The region’s climatology and dynamics are discussed and multiple datasets are considered as potential indices. Agricultural, precipitation, streamflow, remotely sensed vegetation, and Niño sea surface temperature indices were explored as potential bases for index insurance contract. Correlation analyses between the potential geophysical and agricultural indices are examined and two of the rainfall datasets are found to have robust positive correlations with millet production in all three nations, while a particular streamflow index is found to have a robust negative correlation with rice production in Niger. A methodological innovation of this research is the use of Gerrity skill score (GSS) analysis to analyze the indices of high correlation. The correlation and GSS analyses presented here indicate the potential for index insurance using two of the rainfall datasets for the millet crop (drought risk) of all three nations and the Niamey flood month streamflow dataset for the rice crop of Niger (flood risk).

Geography Compass, Jun 1, 2014

Studies of climate change from both natural science and social science disciplines are increasing... more Studies of climate change from both natural science and social science disciplines are increasingly turning their focus to the issue of extreme events. Extreme heat waves, storms, droughts, and coastal inundations pose a disproportionate risk to human life, livelihood, and capital across the world. In the Global South, including Africa, much of the adverse impacts come from hydroclimate extremes as people with limited means are often highly vulnerable to climate shocks. The focus of this review paper will be on hydroclimate extremes in Africa. This paper will consider observations and modeling studies of heat extremes, drought, and flooding from heavy rainfall, along with observations and modeling studies of extreme streamflow events in major rivers and extremes of lake level. This being said, observations of trends in extreme events need to be situated in a context of understanding regional hydroclimate variability. There is tremendous diversity and variability in the hydroclimate of Africa and many extreme events, especially of precipitation and streamflow are associated with patterns of natural variability on a range of time scales.

Proceedings of the National Academy of Sciences of the United States of America, Dec 7, 2015

DCSupplemental. *The question of fat tails in the distribution of damage (5, 6) and more recently... more DCSupplemental. *The question of fat tails in the distribution of damage (5, 6) and more recently the climate impact on growth (7, 8) have also received much attention. † This is one of the two substantive issues in the discounting debate. The other is whether future generations should be given less weight simply because they are in the future. ‡ For instance, the models used by the US Environmental Protection Agency to estimate the social cost of carbon [DICE (12), FUND (13), and PAGE (14); see ref. 15)] do not disaggregate below the level of continental regions. In particular, the entire population of each region is taken to consume the regional average. (And DICE does not disaggregate below the global level.) § This more fine-grained disaggregation of damage and consumption is somewhat analogous to the treatment of heterogeneous emitters in ref. 16, who find that 1 billion high emitters are spread across all the regions of the world. { A similar damage distribution is considered in ref. 17 in the context of the DICE model, but it is not coupled with heterogeneous income as we do here and therefore the impact they get is much smaller in magnitude.

Environmental health perspectives, Aug 17, 2016

Introduction: Climate-economy models known as ‘integrated assessment models’ are widely used by g... more Introduction: Climate-economy models known as ‘integrated assessment models’ are widely used by governments to inform climate policy, including through the estimation of the social cost of carbon. ...

Atmospheric and climate science, 2022

In recent years, there has been increasing demand for high-resolution seasonal climate forecasts ... more In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and health, among others. This paper examines the forecasting skill of the North American Multi-model Ensemble (NMME) over Ethiopia during the June to September (JJAS) season. The NMME, one of the multi-model seasonal forecasting systems, regularly generates monthly seasonal rainfall forecasts over the globe with 0.5-11.5 months lead time. The skill and predictability of seasonal rainfall are assessed using 28 years of hindcast data from the NMME models. The forecast skill is quantified using canonical correlation analysis (CCA) and root mean square error. The results show that the NMME models capture the JJAS seasonal rainfall over central, northern, and northeastern parts of Ethiopia while exhibiting weak or limited skill across western and southwestern How to cite this paper: Teshome, A.,

Climatic Change, Oct 7, 2015

Weather based index insurance is considered to be a potentially promising means of financial adap... more Weather based index insurance is considered to be a potentially promising means of financial adaption to the challenges of climate change and variability; particularly for the agricultural sector in the developing world. However, comparatively little attention has been devoted to the analysis of the long-term viability of this adaptation mechanism in light of the interaction between changes in climate and the frequency of extreme events. Such changes in the frequency of extreme events are expected to have significant implications for the viability and pricing of index insurance over time. This question is analyzed in the context of hypothetical drought and flood index insurance contracts proposed for the West African Sahel using data from five Global Climate Models (GCMs) that were part of the Intergovernmental Panel on Climate Change’s (IPCC) 5th Coupled Model Inter-comparison Project (CMIP5). GCM derived trends in the mean and variance of the regional precipitation are integrated into a Monte Carlo simulation of the frequency of extreme seasonal drought and rainfall. Expected payout risk and the probability of 10 or more payouts in a 30-year window are modeled. The model results presented show significant pricing sensitivity to climate model parameters; particularly changes in the mean precipitation and strong multi-decadal variability. Further, within the Sahel region, there is a significant spatial heterogeneity between sub-regions. These findings imply that the utility and affordability of such index insurance contracts over time will be complex and heterogeneous over time and space.

International Journal of Climatology, Feb 10, 2019

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Climatic Change, Oct 28, 2017

Integrated assessment models (IAMs) of climate and the economy provide estimates of the social co... more Integrated assessment models (IAMs) of climate and the economy provide estimates of the social cost of carbon and inform climate policy. With the Nested Inequalities Climate Economy model (NICE) (Dennig et al. PNAS 112:15,827-15,832, 2015), which is based on Nordhaus's Regional Integrated Model of Climate and the Economy (RICE), but also includes inequalities within regions, we investigate the comparative importance of several factors-namely, time preference, inequality aversion, intraregional inequalities in the distribution of both damage and mitigation cost and the damage function. We do so by computing optimal carbon price trajectories that arise from the wide variety of combinations that are possible given the prevailing range of disagreement over each factor. This provides answers to a number of questions, including Thomas Schelling's conjecture that properly accounting for inequalities could lead the inequality aversion parameter to have an effect opposite to what is suggested by the Ramsey equation.

CCAFS Workshop Reports aim to disseminate interim climate change, agriculture and food security r... more CCAFS Workshop Reports aim to disseminate interim climate change, agriculture and food security research and practices and stimulate feedback from the scientific community.

Malaria Journal

Background Ethiopia has a history of climate related malaria epidemics. An improved understanding... more Background Ethiopia has a history of climate related malaria epidemics. An improved understanding of malaria–climate interactions is needed to inform malaria control and national adaptation plans. Methods Malaria–climate associations in Ethiopia were assessed using (a) monthly climate data (1981–2016) from the Ethiopian National Meteorological Agency (NMA), (b) sea surface temperatures (SSTs) from the eastern Pacific, Indian Ocean and Tropical Atlantic and (c) historical malaria epidemic information obtained from the literature. Data analysed spanned 1950–2016. Individual analyses were undertaken over relevant time periods. The impact of the El Niño Southern Oscillation (ENSO) on seasonal and spatial patterns of rainfall and minimum temperature (Tmin) and maximum temperature (Tmax) was explored using NMA online Maprooms. The relationship of historic malaria epidemics (local or widespread) and concurrent ENSO phases (El Niño, Neutral, La Niña) and climate conditions (including drough...

International Journal of Climatology

The World Bank Economic Review, 2017

How much should present generations sacrifice to reduce emissions today, in order to reduce the f... more How much should present generations sacrifice to reduce emissions today, in order to reduce the future harms of climate change? Within climate economics, debate on this question has been focused on so-called "ethical parameters" of social time preference and inequality aversion. We show that optimal climate policy similarly importantly depends on the future of the developing world. In particular, although global poverty is falling and the economic lives of the poor are improving worldwide, leading models of climate economics may be too optimistic about two central predictions: future population growth in poor countries, and future convergence in total factor productivity (TFP). We report results of small modifications to a standard model: under plausible scenarios for high future population growth (especially in sub-Saharan Africa) and for low future TFP convergence, we find that optimal near-term carbon taxes could be substantially larger.

Atmospheric and Climate Sciences