Section 2: Climate Change and Hydrology
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Item Open Access Spatial changes in climate across Mongolia(Colorado State University. Libraries, 2015-06) Venable, Niah B. H., author; Fassnacht, Steven R., author; Hendricks, Alyssa D., author; Nutag Action and Research Institute, publisherPrevious research using meteorological station data suggests that temperatures and precipitation have been changing more across the semi-arid and arid country of Mongolia than in many other locations across the globe. We used gridded monthly data to determine the annual and seasonal rate of change in total precipitation (P), maximum temperature (Tmax), and minimum temperature (Tmin), as computed from the non-parametric Thiel-Sen slope estimator method. The significance of those changes were computed from the Mann-Kendall test. The University of East Anglia Climatic Research Unit (CRU) dataset was used for the 50-year time period from 1963 through 2012 at a 0.5 degree (~55 km) resolution. For the first 30 years, 30 to 35 meteorological stations from across Mongolia were used to create the spatially distributed "High Resolution Gridded Data of Month-by-Month Variation in Climate" CRU product; 20 to 30 stations were used for the last 20 years due to a decrease in the number of operational stations. Results are presented as maps of 1) mean total annual P, and mean annual Tmax and Tmin, and ii) annual trends over the length of record (1963-2012) with significance overlain, for the three variables. Rates of change at annual and seasonal time scales varied spatially with more consistent increases in temperature; significant precipitation trends were observed over smaller areas than significant temperature trends.Item Open Access How unusual was the 21st century drought in Mongolia?: placing recent extremes in an 1100-year context(Colorado State University. Libraries, 2015-06) Hessl, Amy E., author; Pederson, Neil, author; Byambasuran, Oyunsanaa, author; Anchukaitis, Kevin, author; Leland, Caroline, author; Nutag Action and Research Institute, publisherUnderstanding the connections between climate, ecosystems, and society during historical and modern climate transitions requires annual resolution records with high fidelity climate signals. In the 21st century, Mongolia experienced a rapid transition away from pastoralism as many families lost their herds during a drought and severe winter conditions (dzuds). Though the drivers of this transition were likely multi-factorial, many blamed market forces and overgrazing by herders. Because Mongolia's climate is highly variable, it is difficult to place recent climatic extremes and associated social change in context without long records of climatic variability. Here we ask: how extreme was the 21st century drought in the last 1100 years? We developed a 1100 year long tree-ring reconstruction of warm-season drought, derived from live and dead Siberian pine (Pinus sibirica) trees growing on a Holocene lava flow in north central Mongolia. Trees growing on the lava today are stunted and widely spaced, occurring on microsites with little to no soil development. These trees are water-stressed and their radial growth is correlated with both soil water availability (scPDSI) and grassland productivity (Normalized Difference Vegetation Index (NDVI)). Our reconstruction, calibrated and validated on instrumental June-August scPDSI (1959-2009) account for >57% of the variability in the regional scPDSI when >70% of the annual rainfall occurs. Our tree-ring data combined with meteorological data suggests that the early 21st century drought was the hottest and one of the most severe droughts in the last 1100 years. These results are consistent with model projections of warming in Inner Asia where rising temperatures will contribute to increased water stress, independent of changes in rainfall. Future warming may overwhelm increases in precipitation leading to similar high temperature droughts, with potentially severe environmental and social consequences for modern Mongolia. Long records of past climate variability can help us understand the relative importance of climate versus land management in catalyzing social change and help prepare societies for the full range of future climatic extremes.Item Open Access Earlywood, latewood, and adjusted latewood correlations to precipitation: a test case from the Khangai Mountains, Mongolia(Colorado State University. Libraries, 2015-06) Wolf, J. Marshall, author; Venable, Niah B. H., author; Nutag Action and Research Institute, publisherThe Khangai Mountains of central Mongolia provide important ecosystem services to the surrounding region as the headwaters for a number of river systems and critical pasture for the animal herds of nomadic pastoralists. The mountains also provide a long-term record of regional moisture variability preserved within the tree-rings of Siberian larch (Larix sibirica) forests. Ring width measurements are commonly used to statistically reconstruct the hydroclimatology of a region based on the correlation of ring widths to precipitation and/or streamflow. Tree cores were collected, cross-dated, and the ring widths were measured from a site near Jargalant bagh in northern Bayankhongor aimag. Seasonal precipitation totals for the period from 1962 to 2012 were compiled from several meteorological stations surrounding the site. These historical precipitation values were compared to indices of total (TW), earlywood (EW), and latewood (LW) ring widths generated from a series of 16 cores. Nearly 70% of the annual precipitation in the Khangai region falls during the summer season (June, July, August), resulting in stronger correlations of ring widths (TW, EW and LW) to the previous year's summer precipitation than to the current year's spring or previous year's fall precipitation. The dependence of LW widths on antecedent EW ring widths masks any correlation to spring and fall precipitation. This dependence was removed using linear regression, resulting in the discovery of a negative relationship between the adjusted latewood (LWa) ring widths and precipitation in both spring of the current year and fall of the previous year. This indicates that LWa captures a different climate signal not detectable when working with the original LW, EW or TW measurements. Correlations of EW with (previous year's) summer precipitation were similar in value to correlations of TW with (previous year's) summer precipitation, suggesting that additional measurements of ring width may not be needed for use in reconstructing long-term summer precipitation variability. However, LWa and the associated measurements required for its calculation may be potentially useful for reconstructing spring and fall precipitation patterns in summer precipitation-dominated hydroclimate systems.Item Open Access Characterizing environmental low flows in terms of magnitude, duration and frequency(Colorado State University. Libraries, 2015-06) Kenner, Scott J., author; Nergui, Soninkhishig, author; Sodnom, Tumurchudur, author; Khurelbaatar, Tsogzolmaa, author; Nutag Action and Research Institute, publisherIncreased water demand has led to the need for development of water resources in Mongolia. With the Mongolian government implementation of integrated water resources management approach, assessing environmental flow requirements of major rivers becomes a primary issue. Using Indicators of Hydrological Alteration tools, physical habitat survey at Orkhon-Orkhon gauge site and statistical analysis of annual maximum flows, environmental low flow scenarios have been developed that attempt to reflect more "natural" characteristics of magnitude, frequency and duration. Specifically, minimum seasonal low flows of greater than the 75th percentile flow duration with bankfull flow releases during wet periods that have a duration of 12 to 24 days.Item Open Access A journey down the Tuin: the hydraulics of an internal draining river from the Khangai Mountains to the Gobi Desert(Colorado State University. Libraries, 2015-06) Fassnacht, Steven R., author; Venable, Niah B. H., author; Odgarav, Jigjsuren, author; Sukhbaatar, Jaminkhuyag, author; Adyabadam, Gelegpil, author; Nutag Action and Research Institute, publisherRiver systems flowing through semi-arid and arid regions provide critical ecosystem services for inhabitants of these areas. In remote and/or difficult to access areas away from population centers, few direct measurements exist to characterize the nature of streamflow in these systems. The Tuin River flows from the rugged high mountain and forest steppe landscape of the Khangai Mountains in central Mongolia to its terminus at Orog Lake in the desert steppe and sand dunes of the northern Gobi Desert. Field measurements taken in June 2012 at numerous locations from river headwaters to mouth were used to characterize streamflow in the main river channel and associated floodplain. From these measurements, channel hydraulic characteristics were estimated and hydrologic properties were assessed using a digital elevation model and other spatial data. These properties include contributing area, slope, hydraulic radius, and channel roughness. During the low flow conditions of the survey, streamflow was decreasing from upstream to downstream. At a point between the Bayankhongor and Bogd gaging stations, streamflow ceased at the surface and reappeared approximately 10 kilometres downstream, exemplifying losing flow conditions and subsurface flow components. The results of this analysis could be scalable to other internally draining river systems, especially for hydrologic modelling.