Reduction In Annual Precipitation Research Articles

Bioclimatic Extremes Drive Forest Mortality in Southwest, Western Australia

Extreme and persistent reductions in annual precipitation and an increase in the mean diurnal temperature range have resulted in patch scale forest mortality following the summer of 2010–2011 within the Forest study area near Perth, Western Australia. The impacts of 20 bioclimatic indicators derived from temperature, precipitation and of actual and potential evapotranspiration are quantified. We found that spatially aggregated seasonal climatologies across the study area show 2011 with an annual mean of 17.7 °C (± 5.3 °C) was 1.1 °C warmer than the mean over recent decades (1981–2011,- 16.6 °C ± 4.6 °C) and the mean has been increasing over the last decade. Compared to the same period, 2010–2011 summer maximum temperatures were 1.4 °C (31.6 °C ± 2.0 °C) higher and the annual mean diurnal temperature range (Tmax−Tmin) was 1.6 °C higher (14.7 °C ± 0.5 °C). In 2009, the year before the forest mortality began, annual precipitation across the study area was 69% less (301 mm ± 38 mm) than the mean of 1981–2010 (907 mm ± 69 mm). Using Système Pour l'Observation de la Terre mission 5 (SPOT-5) satellite imagery captured after the summer of 2010–2011 we map a broad scale forest mortality event across the Forested study area. This satellite-climatology based methodology provides a means of monitoring and mapping similar forest mortality events- a critical contribution to our understanding the dynamical bioclimatic drivers of forest mortality events.

Diet and environment of a mid-Pliocene fauna from southwestern Himalaya: Paleo-elevation implications

A mid-Pliocene fauna (4.2–3.1 Ma) was recently uncovered in the Zanda (Zhada) Basin in the southwestern Himalaya, at an elevation of about 4200 m above sea level. These fossil materials provide a unique window for examining the linkage among tectonic, climatic and biotic changes. Here we report the results from isotopic analyses of this fauna and of modern herbivores and waters as well as paleo-temperature estimates from the Zanda Basin. The δ13C values of enamel samples from modern wild Tibetan asses, and domesticated horses, cows and goats in the area are −9.4±1.8‰, which indicate a diet comprising predominantly of C3 plants and are consistent with the current dominance of C3 vegetation in the region. The enamel-δ13C values of the fossil horses, rhinos, deer, and bovids are −9.6±0.8‰, indicating that these ancient mammals, like modern herbivores in the area, also fed primarily on C3 vegetation and lived in an environment dominated by C3 plants. The lack of significant C4 plants in the basin suggests that the area had reached high elevations (>2.5 km) by at least the mid-Pliocene. Taking into account the changes in the δ13C of atmospheric CO2 in the past, the enamel-δ13C values suggest that the average modern-equivalent δ13C value of C3 vegetation in the Zanda Basin in the mid-Pliocene was ∼1–2‰ lower than that of the C3 biomass in the basin today. This would imply a reduction in annual precipitation by about 200–400 mm in the area since then (assuming that the modern C3δ13C–precipitation relationship applied to the past). Consistent with this inference from the δ13C data, the enamel-δ18O data show a significant shift to higher values after the mid-Pliocene, which also suggests a shift in climate to much drier conditions after ∼4–3 Ma.Paleo-temperature estimates derived from a fossil bone-based oxygen isotope temperature proxy as well as the carbonate clumped isotope thermometer for the mid-Pliocene Zanda Basin are higher than the present-day mean annual temperature in the area. After accounting for late Cenozoic global cooling, these paleo-temperature estimates suggest that the paleo-elevation of the Zanda Basin in the mid-Pliocene was similar to or slightly (less than ∼1 km) lower than its present-day elevation, which is consistent with the inference from the δ13C data.

Refugia: keys to climate change management

IntroductionRefugia are habitats that components of biodiversityretreat to, persist in and can potentially expand fromunder changing environmental conditions (Keppelet al., 2012), facilitating the survival of organisms dur-ing extreme climatic changes (Me´dail & Diadema,2009). They may thus maintain favourable climatic con-ditions now absent in the surrounding landscape. Thisis enabled by higher local heterogeneity of micro-climates and the decoupling of local from regionalclimates (Dobrowski, 2011; Keppel et al., 2012).Because refugia potentially safeguard the persistenceof components of biodiversity over millennia, they mayact as safe havens under projected anthropogenic cli-mate change (Me´dail & Diadema, 2009; Keppel et al.,2012). This capacity makes them critical components inclimate change management. As a result, the identifica-tion and protection of refugia has increased in priorityin conservation planning (Noss, 2001; Game et al.,2011). However, refugia are currently loosely definedand their study is often based on ad hoc, descriptivedata sources (Ashcroft, 2010). We therefore clarify theconcept of refugia and related terms. We then argue foran increased focus on understanding how refugia willrespond to climate change. In the context of rapidanthropogenic climate change, we suggest that thisfocus will lead to prioritization of conservation actionstowards those habitats offering the greatest potential assafe havens for biodiversity.What are refugia and what are not?Despite an exponential increase in the use of the termsrefugia and refuges in literature (Fig. 1), refugia are stillconfused with refuges, remnants and reserves. Most cur-rent uses of refugia are to places providing environmen-tal conditions not available in the surroundinglandscapeoverlongperiodsoftime(e.g.,Ashcroft,2010;Dobrowski,2011),withanincreasinginterestinidentify-ing future refugia under projected anthropogenic cli-matechange.However,thetermisalsousedtorefertoavariety of other concepts. For example, in Global ChangeBiology refugia have recently been used to refer totemporary shelter from predation or disturbance (e.g.,Ledger et al., 2011) and to remnant patches of suitablehabitat (e.g., Rittenhouse et al., 2010). The term refugiahas also been used in reference to reserves (see Fig. 1).While thetermrefugiahas onlyrecently beeneffectivelydefined (see Keppel et al., 2012), use of the other threeR-terms has long been widely established. We thereforeadvocatethecorrectuseoftherelevantjargon.Refuges are places that through structures or pro-cesses provide shelter from disturbances, predation,herbivory or competition. They are therefore defined aslocations providing spatial and/or temporal protectionor advantages in biotic interactions over ecological timeperiods (i.e., within the life span of the relevant organ-ism). Remnants are patches of suitable habitats for spe-cies intolerant of changed or modified landscapes thatprevail in landscapes highly modified by human popu-lations and resource exploitation. Reserves are areaslegally or customarily protected from particular anthro-pogenic activities and may vary in size from remnantsto portions of large ‘intact’ landscapes or so-calledwilderness areas.Refugia and anthropogenic climate changeWhile refuges, remnants and reserves continue toreceive considerable research attention, refugia are anarea of rapid recent growth (Fig. 1). The ability of refu-gia to locally mitigate the effects of regional climatechange is increasingly considered important for climatechange adaptation planning (Ashcroft, 2010; Gameet al., 2011). This is because they are potential safehavens for biota and may offer the only hope for in-situpersistence of poorly dispersed species. Protecting suchclimate change refugia could allow some species to

Palaeoecological evidence for the middle and late Holocene vegetation, climate and land use in the upper Don River basin (Russia)

New pollen and plant macrofossil data, backed by radiocarbon dates, from the Kulikovo battlefield area in the forest-steppe region of the Upper Don River basin (central part of European Russia) indicate that the area was covered by mosaic vegetation in the second half of the Holocene. Steppe communities dominated during the mid—late Atlantic (7.2–5.7 cal. kyr b.p.) and early Subatlantic (2.7–2.4 cal. kyr b.p.), while forest-steppe dominated during the Subboreal (2.7–5.7 cal. kyr b.p.), middle and late Subatlantic (2.4 cal. kyr b.p. – present). Climatic reconstructions based on these data show that landscape dynamics in the region were most probably driven by changes in effective moisture: an excess of precipitation over evaporation. Even small reductions in annual precipitation, accompanied by a rise in summer temperatures by 1–3°C above present values, were sufficient to increase the proportion of steppe communities within this landscape complex, and also probably resulted in higher frequencies of wildfires. Signals of anthropogenic disturbance of vegetation are clearly pronounced in the pollen and plant macrofossil records since the middle Atlantic. However, human-induced changes in the vegetation remain subtle until the medieval period.

Response of Russian brome, crested wheatgrass and tall wheatgrass to annual precipitation and grazing management in a semi-arid area

Three grass species, Agropyron desertorum (Agde) and Agropyron elongatum (Agel) and recently, Bromus tomentellus (Brto) are mainly used for range improvement as mixed seeding in semi-arid areas of Iran. Because there is little information about management of these grasses, this study was conducted at the Sisab Research Station in northern Iran to evaluate their responses to grazing management and annual precipitation. Four grazing management treatments were applied for three consecutive years, from 1999 to 2001: no grazing, and light (20-45% forage removal), moderate (45-65% forage removal) and heavy (65-80% forage removal) grazing by lambs and sheep. The fourth year was considered to be a rest from grazing. Data recorded up to fifth years from 1999-2003. The average herbage yield (HY) production across years of Agde (1357 kg/ha) and Agel (1250 kg/ha) was statistically similar, and higher than that of Brto (880 kg/ha). HY decreased with reduction in annual precipitation for all species, especially Agel. Plant number per unit area declined over the study period in all species. Three years of heavy grazing resulted in significant reduction in HY and/or plant number for Brto and Agde, but the rest year compensated for the negative effect of intensive grazing on dry matter production.

Do changes in rainfall patterns affect semiarid annual plant communities?

AbstractQuestion: Climate change models forecast a reduction in annual precipitation and more extreme events (less rainy days and longer drought periods between rainfall events), which may have profound effects on terrestrial ecosystems. Plant growth, population and community dynamics in dry environments are likely to be affected by these changes since productivity is already limited by water availability. We tested the effects of reduced precipitation and fewer rain events on three semiarid plant communities dominated by annual species.Location: Three semiarid plant communities from Almería province (SE Spain).Methods: Rain‐out shelters were set up in each community and watering quantity and frequency were manipulated from autumn to early summer. Plant productivity, cover and diversity were measured at the end of the experimental period.Results: We found that a 50% reduction in watering reduced productivity, plant cover and diversity in all three communities. However, neither the 25% reduction in watering nor changes in the frequency of watering events affected these parameters.Conclusions: The lack of response to small reductions in water could be due to the identity and resistance of the plant communities involved, which are adapted to rainfall variability characteristic of arid environments. Therefore, a rainfall reduction of 25% or less may not affect these plant communities in the short term, although higher reductions or long‐term changes in water availability would probably reduce productivity and diversity in these communities.

Landscape-and-climate dynamics and land use in Late Holocene forest-steppe ecotone of East European Plain (upper Don River Basin case study)

Results of lithological and palynological data of key sequences of the forest-steppe region in the Upper Don River basin, notably, the Kulikovo Battle-Field area, are presented. The obtained evidence shows the occurrence of open forest-steppe and steppe landscape in the Late Holocene. Climate reconstructions failed to demonstrate any drastic changes in the second half of the Holocene. However, even small reductions in annual precipitation, from 400 to 500 mm in the Atlantic, to 300–400 mm in the Subboreal period, accompanied by the rise of summer temperature, from 20–22 °C to 22–24 °C, respectively, were sufficient to cause landscape changes from the forest-steppe to typical steppe. The paper discusses various aspects of human impact on the landscape.

Effect of GCM bias on downscaled precipitation and runoff projections for the Serpentine catchment, Western Australia

AbstractAn investigation has been undertaken to quantify the uncertainty in statistically downscaled catchment precipitation and runoff projections due to different climate models. A significant component of the investigation was the assessment of climate model reproduction of the seasonal (i.e. monthly) cycle of the atmospheric predictors used by a statistical downscaling model. Four climate model simulations forced by the SRES A2 emission scenario were used: the CSIRO Mk3 GCM, the CSIRO Conformal‐Cubic Atmospheric Model (CCAM, run at high spatial resolution over Australia with far‐field forcing from the Mk3 GCM), the Hadley Centre HadAM3P GCM and the Max Planck Institute ECHAM4 GCM.The non‐homogeneous hidden Markov model (NHMM), a stochastic downscaling model, was used to quantify the impacts of the projected climate change on multi‐site, daily precipitation. A catchment water balance model (LUCICAT), calibrated under existing conditions, was driven by the downscaled precipitation to produce runoff projections. Land use and potential evaporation (evapotranspiration potential) were kept fixed for the future climate in order to assess the catchment response to differences in the downscaled precipitation series.Biases in climate model reproduction of the season cycles of the atmospheric predictors used in downscaling are shown to have significant impacts on simulated precipitation, and hence runoff. The downscaled CCAM and Mk3 results project reductions in annual precipitation ranging from 12 to 14% by mid century (2035–2064), resulting in a decline in runoff ranging from 30 to 44%. Downscaling the HadAM3P output, available at the daily time step only for the period 2070–2099, produces a precipitation decline of 24% and a runoff reduction of 69%. The ECHAM4 downscaled precipitation inadequately reproduced the observed annual cycle and so was not used for runoff projection. Copyright © 2007 Royal Meteorological Society

The changes in water-use efficiency and stoma density of Leymus chinensis along Northeast China Transect

Leymus chinensis is a keystone species in the temperate zone grassland of China. Along the NECT (Northeast China Transect) in 2001, water-use efficiency of L. chinensis was analyzed with δ 13C, and changes in the stoma density of its leaves were observed and computed under a microscope. Results showed that the ecological plasticity modulation of the stoma density of L. chinensis and its water-use efficiency were two important mechanisms for its broad ecological adaptability. From east to west along the NECT, the δ 13C of the species varied from -27.49‰ to -23.57‰, consisting with the reduction of annual precipitation, soil water and annual average temperature, but increased with the increase of the elevation of sampling sites. The stoma density increased from 96.9/mm 2 to 169.5/mm 2, indicating that the water-use efficiency for the species was improved along the gradient. The linear coefficient between the two parameters was significant ( R 2 = 0.7338). The results of a stepwise regression analysis showed that the soil water was the first marked factor for determining the stoma density, and the next was the annual precipitation, which suggested that the water factors were the primary ecological factors influencing the stoma density of L. chinensis. The findings in this study showed that the responses of the stoma density and the water-use efficiency for L. chinensis to environmental changes were very complicated. They may be the outcome operated synthetically by all environmental factors in the long-term adaptation to different ecological environments, including human activity, for L. chinensis.

Sediment transferring function of the lower reaches of the Yellow River influenced by drainage basin factors and human activities

Sediment transferring function ( F s ) of rivers is defined and indexed in this study, based on the concept of sediment budget at river reach scales. Then, study is made on the F s of the lower reaches of the Yellow River in relation to natural and human factors in the drainage basin, such as the annual precipitation in different water and sediment source areas, proportion of >0.05 mm sediment of the total sediment load to the lower reaches of Yellow River, the regulated degree of the “clear” baseflow from the drainage area above Lanzhou, frequency of hyperconcentrated flows, area of soil and water conservation measures in the drainage basin. As a result, a multiple regression equation has been established between F s and 7 influencing factors, with multiple correlation coefficient r = 0.90. The reduction in annual precipitation in different water and sediment source areas has different effects on F s . The reduction in annual precipitation in the area above Hekou Town and the area between Longmen and Sanmenxia results in a reduction in F s , but the reduction in annual precipitation in the area between Hekou Town and Longmen results in an increase in F s . The grain size composition of sediment load strongly affects the F s ; the larger the proportion of >0.05 mm sediment in the suspended sediment load entering the lower reaches of the Yellow River is, the lower the F s will be. Thus, if the Xiaolangdi Reservoir traps coarse sediment and releases fine sediment, F s will be enhanced. This study also shows that the lower the proportion of high-flow season river flow to the annual total river flow at Lanzhou Station is, the lower the F s will be. Therefore, the interception of large quantities of clear water by the reservoirs on the upper reaches of Yellow River is one of the major causes for the decrease in Fs in the lower reaches of the Yellow River.

Use of a single-tree simulation model to predict effects of ozone and drought on growth of a white fir tree.

A physiologically based, single-tree simulation model, TREGRO, was parameterized with existing phenological, allometric, and growth data and used to predict effects of ozone and drought on growth of a 53-year-old white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.) tree following a 3-year model simulation. Multiple experimental simulations were conducted to assess the individual and interactive effects of ozone (O(3)) exposure and drought on growth of white fir. The effects of O(3) were imposed as reductions in carbon (C) assimilation of 0, 2.5, 5, 10, and 20%. Drought was imposed as 0, 10, 25, and 50% reductions in total annual precipitation. The results of the simulations were compared with the effects of O(3) on white fir seedlings grown in the presence and absence of ozone in open-top chambers and with a field survey of white fir trees subjected to a gradient of O(3). In the O(3) simulations, an O(3)-induced reduction in C assimilation of 2.5% reduced total tree biomass and branch total nonstructural carbohydrate (TNC) content by < 7%. Although quantifiable in simulation experiments, such small reductions would probably not be detectable in the field. Results from both an open-top chamber experiment and a field survey indicated that reductions in C assimilation of white fir growing in elevated O(3) were much greater than 2.5%, but were not statistically different from control values. A simulated O(3) reduction in C assimilation of >/= 10% reduced total tree biomass by 7% and branch TNC by 55%. Results from the field survey indicated that branch elongation was reduced in response to increased O(3) concentration, corroborating the simulated response of reduced C allocation to the branches of white fir. Although simulated reductions in total annual precipitation of >/= 25% reduced final tree biomass, the simulated reductions also reduced O(3) uptake and therefore reduced the O(3) response of white fir. However, a combination of low amounts of O(3) (2.5% reduction in C assimilation) and drought (25% reduction in annual precipitation) synergistically reduced C gain of white fir more than either stress individually. Our simulations predict that moderate drought (no more than a 25% reduction in total annual precipitation) may not ameliorate the response of white fir to O(3) and that moderate amounts of atmospheric O(3) and drought could be more detrimental to white fir than either stress singly.

Regional climate change impacts: II. Impacts on water management works

Abstract The sensitivity of some critical water management issues, such as reservoir storage and hydroelectric production, to climatic variability and change on a regional basis is analysed and presented. This is the second of two papers presented in this issue dealing with the regional hydrological effects of climatic change. By using a set of plausible hypothetical climatic scenarios to represent both greenhouse warming and precipitation changes, the sensitivity of the guaranteed annual fresh water and energy supply levels has been evaluated under conditions of altered runoff for four connected multi-purpose reservoirs in central Greece. It is shown that reservoirs designed and operated under current climatic conditions are, in general, affected by the climatic changes examined. A dramatic increase of the risk associated with the annual guaranteed quantity of water supply and energy production would occur if greenhouse warming were accompanied by a reduction in annual precipitation. Significant increase...