Summer Precipitation Regime Research Articles

Soybean Response to Drainage and Subirrigation on a Claypan Soil in Northeast Missouri

Integrated water management systems using drainage plus subirrigation (DSI) have reduced nitrate‐loading of drainage water flow and may increase soybean [Glycine max (L.) Merr.] yield. Shallow drain tile depths and narrow spacings are recommended for claypan soils. Field research (2003–2006) evaluated the effects of drainage (DO) and DSI on planting date and the effects of DO and DSI at 6.1 and 12.2 m spacings on soybean yield compared to nondrained (ND) and nondrained delayed planting (NDDP) controls on claypan soils. Soybean were planted up to 17 d earlier with DO or DSI systems. Plant populations were reduced 29 to 52% in the nondrained control due to poor drainage in 3 of the 4 yr. Grain yield, water applied through the DSI system, and water level depth were similar at a 6.1 or 12.2 m drain tile spacing. Average yield increase with DSI at 6.1 and 12.2 m spacings was 12 to 29% (410–910 kg ha−1) while DO at the same spacings increased yield 9 to 22% (300–710 kg ha−1) compared to ND or NDDP controls. In a dry year (2005), drainage plus subirrigation increased yield up to 1200 kg ha−1 compared to DO. Plant population variability at harvest was lower with the DO or DSI systems compared to ND or NDDP controls. Yield variability over the 4 yr was lower with DSI compared with DO or ND controls, which was affected by the spring–summer precipitation regimes and is important to farmers for a more predictable soybean marketing strategy.

Semiarid watershed response in central New Mexico and its sensitivity to climate variability and change

Abstract. Hydrologic processes in the semiarid regions of the Southwest United States are considered to be highly susceptible to variations in temperature and precipitation characteristics due to the effects of climate change. Relatively little is known about the potential impacts of climate change on the basin hydrologic response, namely streamflow, evapotranspiration and recharge, in the region. In this study, we present the development and application of a continuous, semi-distributed watershed model for climate change studies in semiarid basins of the Southwest US. Our objective is to capture hydrologic processes in large watersheds, while accounting for the spatial and temporal variations of climate forcing and basin properties in a simple fashion. We apply the model to the Río Salado basin in central New Mexico since it exhibits both a winter and summer precipitation regime and has a historical streamflow record for model testing purposes. Subsequently, we use a sequence of climate change scenarios that capture observed trends for winter and summer precipitation, as well as their interaction with higher temperatures, to perform long-term ensemble simulations of the basin response. Results of the modeling exercise indicate that precipitation uncertainty is amplified in the hydrologic response, in particular for processes that depend on a soil saturation threshold. We obtained substantially different hydrologic sensitivities for winter and summer precipitation ensembles, indicating a greater sensitivity to more intense summer storms as compared to more frequent winter events. In addition, the impact of changes in precipitation characteristics overwhelmed the effects of increased temperature in the study basin. Nevertheless, combined trends in precipitation and temperature yield a more sensitive hydrologic response throughout the year.

Changing fire regimes in the temperate rainforest region of southern Chile over the last 16,000 yr

A high-resolution macroscopic charcoal record from Lago Melli (42°46′S, 73°33′W) documents the occurrence of forest fires in the lowlands of Isla Grande de Chiloé, southern Chile, over the last 16,000 yr. Our data suggest that fire activity in this region was largely modulated by the position/intensity of the southern westerlies at multi-millennial time scales. Fire activity was infrequent or absent between 16,000–11,000 and 8500–7000 cal yr BP and was maximal between ∼ 11,000–8500 and 3000–0 cal yr BP. A mosaic of Valdivian/North Patagonian rainforest species started at ∼ 6000 cal yr BP, along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr BP. The modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability, suggesting the onset of high-frequency variability in summer precipitation regimes starting at ∼ 5500 cal yr BP. Because negative anomalies in summer precipitation in this region are teleconnected with modern El Niño events, we propose that the onset of El Niño-like variability at ∼ 5700–6200 cal yr BP led to a reshuffling of rainforest communities in the lowlands of Isla Grande de Chiloé and an increase in fire activity.

Late Quaternary glacial history in the Encierro Valley, northern Chile (29°S), deduced from 10Be surface exposure dating

The Late Pleistocene glacial and climate history in the dry Central Andes is not well known so far, mainly because of the lack of suitable material for radiocarbon dating. In order to establish a glacial chronology, we applied surface exposure dating, using in-situ produced cosmogenic 10Be, for 11 boulders from moraines in the Encierro Valley (29°S), northern Chile. We discuss sample-specific effects (topographic shielding, sample geometry, rock surface erosion, inheritance and post-depositional geomorphological instability) and systematic uncertainties (production rate of 10Be, latitude and altitude scaling). Minor glacial advances probably occurred around 11.6 ± 1.2 ka BP, whereas major advances are recorded at 14.0 ± 1.4 ka BP and eventually at 24.1 ± 2.4 ka BP. This may indicate synchrony of some Late Pleistocene glacial advances south and north of the so-called Arid Diagonal (∼ 25°S). Increased precipitation plays a dominant role for the observed Late Pleistocene glacial advances. In the absence of further glacial chronologies south and north of the research area, it remains difficult to disentangle the influence of the complex and in space and time variable westerlies and the tropical summer precipitation regime.

A Feature-Based Approach to Satellite Precipitation Monitoring Using Geostationary IR Imagery

Abstract This paper describes a new geostationary infrared satellite precipitation monitoring methodology that draws on techniques from machine vision to develop a mathematical representation of cloud shapes and textures and the form of their embedding meteorological context. Quantitative feature descriptions derived from Geostationary Operational Environmental Satellite (GOES) band-4 infrared imagery were translated into 15-min precipitation estimates through the use of an artificial neural network. The network was trained using 3-hourly ground-radar data in lieu of a dense constellation of polar-orbiting spacecraft such as the proposed Global Precipitation Measurement (GPM) mission. The technique has been tested using data from the Texas–Florida Underflights Experiment (TEFLUN-B) and has demonstrated significant advantages over existing satellite precipitation monitoring techniques when applied to a summer precipitation regime in Florida.

Low‐level jets and the summer precipitation regimes over North America

The summer precipitation regimes over the United States and their relation to two low level jets are examined using a daily gauge‐based precipitation data set, the NCEP‐NCAR reanalysis and the 10‐yr summer (June–September) simulations based on the 50‐km NCEP regional spectral model (RSM) with the initial and boundary conditions provided by the global reanalyses. The quality at regional scales of the RSM simulations is assessed through the comparison with the NCEP's operational Eta Data Assimilation System (EDAS) analyses. The RSM, as EDAS, captures the seasonal evolution of the North American monsoon rainfall and the related vertically integrated moisture fluxes, but details differ. The fluxes associated with the Great Plains low level jet (GPLLJ) and the Gulf of California low level jet (GCLLJ) depicted by the two data sets are similar, but the 50‐km RSM has difficulty in capturing the vertical structure of the meridional moisture flux associated with the GCLLJ. The recurrent summer precipitation regime is a three cell pattern that consists of an inverse phase relationship between the Great Plains and the core monsoon region with an additional weak center over the southeastern United States. Over the southwestern United States, Arizona and New Mexico belong to two different rainfall regimes and have different moisture sources. The out of phase precipitation relationship is consistently related to an out of phase relationship between the two LLJs, whose variations are in turn associated with the upper level jet streams. The strong GCLLJ cases imply a weaker GPLLJ and less rainfall over the central United States and the Mississippi Valley. The strong GPLLJ cases only imply weaker meridional moisture fluxes from northern Mexico or Gulf of California to the southwestern United States and less monsoon rainfall there, but they do not have an impact on moisture fluxes along the Gulf of California.

A test of the relationship between seasonal rainfall and saguaro cacti branching patterns

Reproductive output, as well as photosynthetically active radiation interception and CO2 uptake, increase as saguaro cacti Carnegiea gigantea (Engelm.) Britt. and Rose branch, and branching increases with increasing moisture. The Sonoran Desert experiences distinct summer and winter precipitation regimes that vary in both geography and scale. Many aspects of saguaro ecology are known to depend on the summer rains, which has resulted in an emphasis on summer rains in the literature. Similarly, branching studies have been limited geographically to areas that receive relatively high amounts of summer rainfall. These studies, therefore, attribute branching patterns to the summer (or possibly annual) rains, and conclusions reflect the summer precipitation bias. Environmental variability in space was explored in the present study to investigate saguaro branching patterns. I collected height and branching data in thirty saguaro populations across their American range. Stepwise regression was used to determine which climate, vegetation and soil variables best predict branching. Contrary to the literature, this study found that winter precipitation, particularly from January to April, was the best predictor of branching, not summer or annual rain. Surprisingly, the relationship between the summer monsoons (July and August precipitation) and branching was negative. This is likely due to the fact that summer and winter rainfall patterns are geographically distinct. Winter precipitation appears to play a key role in branching, and thus in seed production. This suggests that saguaros benefit from moisture during the winter, possibly utilizing cold‐season rains for increasing their reproductive output through branching, and challenging the view that the summer rains dominate virtually every aspect of the saguaro life‐cycle, and creating a more balanced view of saguaro ecology.

Records of Late Pleistocene–Holocene climatic change in Mexico — a review

Here we review palaeoclimatic records from Mexico which have a reasonable chronological framework and are readily accessible. Reconstructions are based on pollen, diatoms, sediment chemistry and isotopes, packrat middens and glacial records and are discussed within the context of Central Mexico, the Yucatan and Northern Mexico, the three regions for which significant information is available. The available data indicate that over the Late Pleistocene and Holocene there have been significant climatic changes in Mexico, although smaller in magnitude than in other parts of the northern hemisphere tropics and subtropics. Maps of conditions at 18,000, 9000, 6000, 5000 and 1000 yr BP are presented. These show that northern Mexico and the Yucatan often show opposite climatic signals, whilst the highlands of central Mexico are more variable. Around the Last Glacial Maximum it seems that the modern summer precipitation regime had collapsed. Northern Mexico, however, was much wetter than today due to increased winter rainfall. Modern rainfall patterns were not fully established until after 9000 yr BP and generally wet conditions prevailed about 6000 yr BP. The mid-Holocene seems to have been a period of great climatic variability with a number of records showing oscillations between 6000 and 5000 yr BP. A period of marked aridity is recorded in the Yucatan and central Mexico about 1000 yr BP. More well-dated, continuous records are needed, especially covering the last glacial–interglacial transition. The changing balance between temperate and tropical climate systems and the influence of the Pacific compared with the Gulf of Mexico/Caribbean warrant further investigation.

Dominant Factors Responsible for Interannual Variability of the Summer Monsoon in the Southwestern United States

Interannual variability of the summer monsoon in the southwestern United States is controlled by various ocean- and land-based conditions (e.g., SST, soil moisture, and snow cover) that provide sources of memory of antecedent climate anomalies such as ENSO. It is hypothesized that this interannual variability is also modulated by decade-scale fluctuations in the North Pacific SSTs. The following observations have been made in support of this hypothesis. First, the summer precipitation regime is dominated by a continental-scale precipitation pattern characterized by an out-of-phase relationship between precipitation in the southwestern United States and that in the Great Plains of the United States. Second, interannual fluctuations in the onset date of the monsoon in the southwestern United States are significantly correlated with interannual fluctuations in the intensity of summer rainfall in this region such that early monsoons are often very wet and late monsoons tend to be dry. Third, wet (dry) monsoons in the southwestern United States often follow winters characterized by dry (wet) conditions in the southwestern United States and wet (dry) conditions in the northwestern United States. Finally, interannual variability of the summer monsoon in the southwestern United States is modulated by long-term (decade scale) fluctuations in the North Pacific SSTs. The mechanism relating the North Pacific SST pattern to interannual variability in the summer monsoon appears to be via the impact of variations in the Pacific jet on West Coast precipitation regimes during the preceding winter. Multiyear fluctuations in the North Pacific SST pattern are consistent with multiyear fluctuations in the atmospheric circulation and in the West Coast precipitation regimes during Northern Hemisphere (NH) winter, hence with multiyear variability in the summer monsoon state. Influences on the summer monsoon during the preceding winter and spring are tied together using appropriate SST indices that capture decade-scale variability in the North Pacific during NH winter and interannual variability in the eastern tropical Pacific during NH spring. The results suggest that decadal variability in the North Pacific SSTs may be an important factor in determining long-term periods of summertime drought or rainy conditions both in the southwestern United States and in the Great Plains of the United States.

Interannual Variability of the U.S. Summer Precipitation Regime with Emphasis on the Southwestern Monsoon

Abstract Relationships between the interannual variability of the U.S. summer precipitation regime and the intensification, weakening, or changes in position of the climatological-mean circulation features that organize this regime are examined. The focus is on the atmospheric conditions over the conterminous United States relative to wet and dry monsoons over the southwestern United States. The onset of the monsoon in this region, which typically begins in early July, is determined using an index based on daily observed precipitation for a 32-yr (1963–94) period. Composites of observed precipitation and various fields from the National Centers for Environmental Prediction–National Center for Atmospheric Research Reanalysis for wet and dry monsoons are used to show that the interannual variability of the summer precipitation regime closely mimics the seasonal changes associated with the development of the North American monsoon system. The warm season precipitation regime is characterized by a continental...

Principal components-based regionalization of precipitation regimes across the southwest United States and Northern Mexico, with an application to monsoon precipitation variability

We determine precipitation regions for the United States-Mexico border region based on seasonality and variability of monthly precipitation at 309 stations for the period 1961 to 1990. Using a correlation matrix of input data to avoid the effect of elevation on precipitation, we apply principal components analysis with oblique rotation to regionalize this large, climatologically complex study area. We examine the applicability of the method, 2 techniques for defining region boundaries, the various defined regions themselves, and the effects of transforming input data and changing obliquity of component rotation. We obtain 9 consistent and largely contiguous regions from each of the analyses, including regions for the North American monsoon, the low deserts, the California Mediterranean regime, and for summer precipitation regimes adjoining the Gulf of Mexico. The derived regions and associated boundaries make physical sense in terms of the driving atmospheric processes, and they are robust to transformed input data and changes in rotation procedures. The central border regions are remarkably consistent across analyses, with small changes to peripheral regions. We also identify 4 monsoon sub-regions, and we illustrate the applicability of the regionalization via an analysis of relationships between monsoon precipitation variability and 500 mb pressure heights. Significantly different 500 mb circulation patterns are associated with wet and dry monsoon seasons in each of the subregions, and it appears that shifts in 500 mb circulation relative to the geographic position of each sub-region influence seasonal precipitation variability, directly or indirectly. There are important differences between some sub-regions, but in general wet monsoons are associated with northward meridional bulging of the subtropical anticyclone over the continental monsoon areas, while dry monsoons are associated with zonal stretching of the subtropical anticyclone over adjacent oceans with slightly higher pressure-heights. Overall, the study provides a clear regionalization of the precipitation climatology for the southwest United States and northern Mexico, and shows its utility for studies of climate variability.

Influence of the North American Monsoon System on the U.S. Summer Precipitation Regime

Abstract Key features of the U.S. summer precipitation regime are examined within the context of the evolving North American monsoon system. The focus is on the antecedent and subsequent atmospheric conditions over the conterminous United States relative to the onset of monsoon precipitation over the southwestern United States, which typically begins in early July. The onset of the monsoon in this region is determined using a precipitation index, based on daily observed precipitation for a 31-yr (1963–94) period. Lagged composites of the observed precipitation and various fields from the NCEP–NCAR reanalysis for the period 1979–94 provide a comprehensive picture of atmospheric conditions during the evolution of the U.S. warm season precipitation regime. The summer precipitation regime is characterized by an out-of-phase relationship between precipitation over the Southwest and the Great Plains–northern tier and an in-phase relationship between precipitation over the Southwest and the East Coast. Changes i...

Seasonal variation and annual fluctuation in granite outcrop plant communities

Permanent quadrats in granite outcrop plant communities allowed us to monitor seasonal variation and annual fluctuation in community structure. Seasonal species turn-over was significant in communities on shallow soil, but not in communities on deeper soil where seasonal dominance shifts were common. Exceptional meteorological events appeared to mediate phenomena of competitive release in some island communities. A decrease in the abundance of Arenaria uniflora in Lichen-annual island communities, following a spring drought, was correlated with an increase in the abundance of Sedum smallii, a shallower-soil species. Richness in Annual-perennial island communities was higher in spring 1985 than in 1984 or 1986, and this occurred as the dominant species, Senecio tomentosus, temporarily declined in importance following a severe drought in late summer 1984. Significant annual fluctuation in the cover of Viguiera porteri could also be related to variations in the summer precipitation regime. Overall, plant responses to drought were individualistic and depended largely on the timing of these meteorological events in relation to the life-stages and/or the physiological status of the plants.

Water balance of Britain, 50,000 yr B.P. to the present day

Estimates made of lowland precipitation and evaporation in Britain during the last (Devensian) glaciation suggest that during the cold periods of the Devensian precipitation was probably low, between 260 and 370 mm/year, with winter precipitation between 80 and 120 mm, whereas at the thermal maximum of the Upton Warren Interstadial lowland precipitation was probably in the range 450 to 650 mm/year. Two summer precipitation regimes are identified during the cold periods, one with high values and the other with low. The high summer precipitation variant leads to moist conditions with July and August precipitation values similar to those at the present day, and global circulation models suggest that the moist regime may have existed at the time of the maximum advance of the ice sheets. On the other hand, the low summer precipitation variant leads to a dry summer with wind action creating aeolian deposits, and this variant probably existed at earlier times in the glacial period. About 6500 yr B.P., in the Atlantic period, forest conditions probably caused increased evaporation which more than compensated for the increased precipitation of the time, causing low runoff conditions. The clearance of British forests by man since 6500 yr B.P. has probably led to an absolute increase in runoff values even though precipitation values have fallen.

The June-July Precipitation Pattern in the Prairie Provinces of Canada

Abstract Few studies exist which deal with the synoptic climatological explanation of precipitation problems in the Canadian Prairies. Under particular consideration is the summer precipitation regime in the Prairie Provinces of Canada which is so significant for the cultivation of spring wheat. An attempt has been made to explain the June-July precipitation in the interior plains of Canada in terms of surface and upper atmospheric flow patterns. A unique feature of the precipitation pattern is that while in the southern half of this area, June is the month of maximum precipitation, in the northern half it is July. The investigation reveals that this interesting precipitation regime is related to the unusual extension of the Pacific High Pressure cell towards the northeast and a northward displacement of jet streams, frontal zones, and cyclonic tracks.