Drier Future Climate Research Articles

A tree-ring reconstruction of streamflow in the Santa Fe River, New Mexico

Summary The upper Santa Fe River provides up to 50% of the water supply for the growing population of Santa Fe, NM. Recent droughts have dramatically lowered reservoir levels and raised concern about the future of the water supply, particularly when combined with projections of a warmer and drier future climate. In this study, new and updated tree-ring chronologies are used to reconstruct annual discharge for the upper Santa Fe River and place the short period of gaged flows, 1914–2007, in a long-term context. Principal components analysis and forward stepwise multiple linear regression were used to produce two reconstructions: (1) a better fit, “short reconstruction” (adjusted R2 = 0.62, 1592–2007) and (2) a less robust, “long reconstruction” (adj. R2 = 0.50, 1305–2007). Both reconstructions indicate that recent extreme low flow events (e.g., 2002) are rare (5th percentile) in the long-term records and that the 1950s drought contained the lowest 7-year mean flows over the past 400–700 years. However, longer, multi-decadal dry periods not present in the gaged flows occurred in the past. For example, the 40-year mean for 1544–1583 is estimated at just 86% of the 1914–2007 mean. During extended dry periods in the 16th and 18th centuries the probability that annual flow would not meet the current surface water allocation and instream flow target (7.52 million cubic meters, MCM) was up to 10% greater (78.7% non-exceedence probability) than during the instrumental period. The results indicate that the gaged record does not contain the full range of high and low flows or the variability in the probability distributions of flows present in the long-term record. Therefore current and future water management and planning based on the instrumental period may not adequately buffer against the natural variability in the climate and streamflow systems. This valuable paleo-hydrologic information is in the process of being incorporated into water supply planning for the City of Santa Fe (e.g., modeling future water supply scenarios directly from reconstructed periods of streamflow).

Hydrological response of a Brazilian semi‐arid catchment to different land use and climate change scenarios: a modelling study

AbstractBrazilian semi‐arid regions are characterized by water scarcity, vulnerability to desertification, and climate variability. The investigation of hydrological processes in this region is of major interest not only for water planning strategies but also to address the possible impact of future climate and land‐use changes on water resources. A hydrological distributed catchment‐scale model (DiCaSM) has been applied to simulate hydrological processes in a small representative catchment of the Brazilian northeast semi‐arid region, and also to investigate the impact of climate and land‐use changes, as well as changes associated with biofuel/energy crops production. The catchment is part of the Brazilian network for semi‐arid hydrology, established by the Brazilian Federal Government. Estimating and modelling streamflow (STF) and recharge in semi‐arid areas is a challenging task, mainly because of limitation in in situ measurements, and also due to the local nature of some processes. Direct recharge measurements are very difficult in semi‐arid catchments and contain a high level of uncertainty. The latter is usually addressed by short‐ and long‐time‐scale calibration and validation at catchment scale, as well as by examining the model sensitivity to the physical parameters responsible for the recharge. The DiCaSM model was run from 2000 to 2008, and streamflow was successfully simulated, with a Nash–Sutcliffe (NS) efficiency coefficient of 0·73, and R2 of 0·79. On the basis of a range of climate change scenarios for the region, the DiCaSM model forecasted a reduction by 35%, 68%, and 77%, in groundwater recharge (GWR), and by 34%, 65%, and 72%, in streamflow, for the time spans 2010–2039, 2040–2069, and 2070–2099, respectively, could take place for a dry future climate scenario. These reductions would produce severe impact on water availability in the region. Introducing castor beans to the catchment would increase the GWR and streamflow, mainly if the caatinga areas would be converted into castor beans production. Changing an area of 1000 ha from caatinga to castor beans would increase the GWR by 46% and streamflow by 3%. If the same area of pasture is converted into castor beans, there would be an increase in GWR and streamflow by 24% and 5%, respectively. Such results are expected to contribute towards environmental policies for north‐east Brazil (NEB), and to biofuel production perspectives in the region. Copyright © 2010 John Wiley & Sons, Ltd.

Temperate forest herbs are adapted to high air humidity — evidence from climate chamber and humidity manipulation experiments in the field

How growth and morphology of wild plants are controlled by the water vapor saturation deficit of the air (vapor pressure deficit, VPD) is not sufficiently understood. We tested the hypothesis that VPD acts on temperate woodland herbs independently from soil moisture by exposing two species ( Mercurialis perennis L. and Stachys sylvatica Torr.) to variable VPD levels in climate chambers and in open-top chambers on the forest floor. A decrease in air humidity from 85% to 40% in the climate chamber experiment, which simulates a microclimate change after canopy gap creation, resulted in a 40% decrease in biomass production of both species when grown in hydroponic culture. This result is supported by the more realistic open-top chamber experiment, which showed a productivity decrease by approximately 25% when plants were continuously exposed to an atmosphere with 15% lower air humidity than ambient. Elevated VPD levels reduced biomass production through either a reduced leaf expansion rate or a lower number of formed leaf buds. We conclude that many woodland herbs require sufficiently high air humidity for optimal growth; permanently decreased air humidity, as may occur in a future drier climate, after gap creation, or after clear-cutting of the forest, may threaten the vitality and survival of woodland herbs.

Spatial variation in temperature thresholds during seed germination of remnant Festuca hallii populations across the Canadian prairie

Grassland in North America is expected to expand northward as the climate becomes warmer and drier under many climate change scenarios. Successful adaptation of plant species to climate change depends on regeneration success. This paper aims to identify the spatial variation in seed germination characteristics of Festuca hallii populations and to quantify the effect of genetic, geographic, demographic, or climatic factors on the variation. Seeds were collected from 15 populations in five ecoregions over a wide geographic range in Canada. Seeds were germinated at 7 growth chambers with constant temperatures from 5 to 35 °C with 5 °C increments. Thermal time models were constructed to generate germination thresholds. Correlations between germination parameters and genetic variation, longitude, latitude, population size, geographic distance to the nearest neighbour, mean annual temperature (MAT) and mean annual precipitation (MAP) were assessed. Base temperatures ( T b , minimal or base temperature permitting germination) of the 15 populations fell into a narrow range within 2.2 °C with an average of 1.1 °C. T b was positively correlated with latitude and negatively with longitude and the thermal time requirement for 50% germination was negatively correlated with latitude. Seed mass was negatively correlated with MAT and positively correlated with MAP. High final germination percentage was reached at a wide temperature range from 5 to 20 °C with the highest germination percentage at 10 °C. Germination rate index (GRI) increased with increasing temperature from 5 to 20 °C. Final germination percentage at 5 °C was negatively correlated with MAT and positively correlated with MAP. GRIs at 5 and 10 °C were positively correlated with MAP but not with MAT. GRI at 5 °C was positively correlated with longitude. Germination was not correlated with any genetic and demographic attributes assayed. Population-wise variation in temperature and precipitation affects seed mass, an important attribute determining seed germinability. Sites with greater precipitation and lower temperature had heavier seeds, which usually had lower thermal time requirements for germination and faster germination. The warmer and drier future climate as predicted for the Canadian prairie may reduce regeneration success of this species in the current distribution range, particularly after disturbances followed by sexual regeneration from seeds.

Towards a climate change adaptation strategy for coffee communities and ecosystems in the Sierra Madre de Chiapas, Mexico

The mountain chain of the Sierra Madre de Chiapas in southern Mexico is globally significant for its biodiversity and is one of the most important coffee production areas of Mexico. It provides water for several municipalities and its biosphere reserves are important tourist attractions. Much of the forest cover outside the core protected areas is in fact coffee grown under traditional forest shade. Unless this (agro)forest cover can be sustained, the biodiversity of the Sierra Madre and the environmental services it provides are at risk. We analyzed the threats to livelihoods and environment from climate change through crop suitability modeling based on downscaled climate scenarios for the period 2040 to 2069 (referred to as 2050s) and developed adaptation options through an expert workshop. Significant areas of forest and occasionally coffee are destroyed every year by wildfires, and this problem is bound to increase in a hotter and drier future climate. Widespread landslides and inundations, including on coffee farms, have recently been caused by hurricanes whose intensity is predicted to increase. A hotter climate with more irregular rainfall will be less favorable to the production of quality coffee and lower profitability may compel farmers to abandon shade coffee and expand other land uses of less biodiversity value, probably at the expense of forest. A comprehensive strategy to sustain the biodiversity, ecosystem services and livelihoods of the Sierra Madre in the face of climate change should include the promotion of biodiversity friendly coffee growing and processing practices including complex shade which can offer some hurricane protection and product diversification; payments for forest conservation and restoration from existing government programs complemented by private initiatives; diversification of income sources to mitigate risks associated with unstable environmental conditions and coffee markets; integrated fire management; development of markets that reward sustainable land use practices and forest conservation; crop insurance programs that are accessible to smallholders; and the strengthening of local capacity for adaptive resource management.

Growth of European beech ( Fagus sylvatica L.) saplings is limited by elevated atmospheric vapour pressure deficits

There is an ongoing debate about how European beech might be affected by a future drier climate. While numerous studies have examined the effects of soil drought on beech growth and development, studies investigating the effects of elevated atmospheric water vapour pressure deficit (VPD) are lacking. By increasing VPD in climate and open-top chamber experiments, with moisture in the rooting medium near optimum, we tested the hypothesis that increased VPD negatively affects the growth and development of European beech saplings. In the climate chambers, a reduction in relative air humidity by 40% resulted in a 68% reduction in productivity. Similarly, in the open-top chamber experiment conducted on the forest floor, biomass declined by 30% when relative air humidity was 15% lower. The reduction in biomass was mainly a consequence of a dramatically reduced leaf growth of beech in the elevated VPD treatments. Our results show that growth and development of beech saplings strongly depend not only on soil moisture but also on the prevailing VPD level. We conclude that the vapour pressure deficit is a widely ignored factor which influences the growth and vitality, and possibly also the distribution of European beech. Future forest management schemes under an altered climate should take this factor into account.

Testing statistical downscaling methods in simulated climates

The consistency of two statistical downscaling methods and two different predictors to estimate past (last millennium) and future (21st century) precipitation in the Iberian and Scandinavian Peninsulas is assessed in the surrogate climate of a coupled climate model simulation. The methods are based on canonical correlation analysis and the search for analogs, with sea level pressure (SLP) and 500 mb geopotential height as predictors. The precipitation downscaled by the statistical methods within the simulated climate is compared with the direct model output. The estimation based on SLP alone agrees with the modeled precipitation on the Iberian Peninsula. However, the estimates for Scandinavia in the 21st century are drier than the target precipitation. Geopotential height as predictor performs worse than SLP in both regions yielding too dry future climate. Differences in both regions are analyzed in terms of relative humidity, which contributes to future precipitation changes of Scandinavian precipitation.

Forest change on a steep mountain gradient after extended fire exclusion: San Francisco Peaks, Arizona, USA

Summary More than a century of forest management, including fire exclusion, livestock grazing and tree harvesting, may have affected forest structure and composition in south‐western USA. Dendroecological techniques were used to reconstruct an 1876 baseline against which modern conditions could be compared. We assessed the magnitude of changes on the San Francisco Peaks in five distinct forest types: ponderosa, mixed conifer, aspen, spruce–fir and bristlecone. We established a systematic grid of 135 plots, each 0·1 ha in size, over a 1117‐m altitudinal band. In the contemporary forest, density was greatest in spruce–fir and least in bristlecone whereas basal area was greatest in spruce–fir and lowest in ponderosa. In 1876, all forest types had significantly lower densities and basal areas. The period since 1876 was associated with increased forest density, a shift in species composition as a result of invasion of shade‐tolerant conifers, and a trend for mesic species to migrate to lower altitudes. Changes were least evident in the highest altitude forests. Climate and human‐caused and natural biotic disturbance factors probably all played a role in forest change, but we argue that the most prominent factor was probably exclusion of the thinning effect of fire, especially on fire‐susceptible mesic species. Synthesis and applications. Mesic species have encroached to lower altitudes and forest density has increased since 1876. These changes have created to conditions opposite to those suitable for warmer, drier future climates that will display increased fire risk, setting the stage for sudden and severe change. Management is complex because of heavy fuel loading, administrative constraints and high public visibility. However, ‘sky island’ landscapes such as the Peaks represent protected ecosystems of great importance in arid regions. Testing of wildland fire use and other management interventions to restore composition and fuel structures more resilient to warmer climate should proceed.