Preseason Precipitation Research Articles

Improved mapping and change detection of the start of the crop growing season in the US Corn Belt from long-term AVHRR NDVI

Long-term monitoring of crop phenology is a critical process to understand changes in cropland vegetation dynamics related to climate and human management. During the last four decades, seasonal changes in vegetation have been measured by satellite instruments, the Advanced Very High Resolution Radiometers (AVHRRs). However, an acceptable detection of crop phenology has been prevented due to its coarse spatial resolution (~8 km) pixels in which croplands are frequently mixed with non-cropland. This study introduces a novel method for detecting the start of the growing season in cropland (SOSC) from the AVHRR Normalized Difference Vegetation Index (NDVI) to examine the long-term changes in SOSC at the 8-km pixel level across the core cropping regions of the Midwestern United States (the so-called ‘the Corn Belt’) for 1982–2015. The AVHRR-based SOSC was compared with the SOSC retrieved from the pixels covering mostly croplands of the 250-m Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI. These two satellite-based SOSC shows reasonable correspondence in spatial patterns so that the annual values of the root mean square difference ranges from 3.6 to 7.4 days during the overlapping period of 2008–2015. Also, an acceptable correspondence was found between the interannual variations in the AVHRR SOSCs and in the state-level survey of crop stages. For sowing stages, correlation coefficients ranged from 0.43 to 0.68; for flowering stages those ranged from 0.51 to 0.83. By analyzing long-term SOSC changes with climate factors, we found a strong tendency that warmer pre-season condition is accompanied with earlier SOSC. In addition, larger pre-season precipitation tends to postpone SOSC as strongly as the pre-season temperature affects SOSC in a considerable portion of the core cropland. This study suggests that the postponing of sowing due to larger precipitation, which has rarely been highlighted in previous studies, requires more attentions in order for better understanding of vegetation dynamics in agriculture-climate studies.

Phenological changes in herbaceous plants in China's grasslands and their responses to climate change: a meta-analysis.

Plant phenological events are sensitive indicators of climate change, and their change could markedly affect the structure and function of ecosystems. Previous studies have revealed the spatiotemporal variations in the phenological events of woody plants. However, limited studies have focused on the phenophases of herbaceous plants. In this study, by using a meta-analysis method, we extracted information about the phenological changes in herbaceous plants in China's grasslands from existing studies (including the period, station, species, phenophases, phenological trends, and climatic determinants) and analyzed the patterns manifested in the dataset. The results showed that the spring phenophases (e.g., first leaf date and first flowering date) of the herbaceous plants mainly advanced over the past 30years, but a large difference existed across grassland types. The spring phenophases of forages (species from the Cyperaceae, Gramineae, and Leguminosae families) became earlier in the desert steppe and alpine steppe but showed no apparent trends in the alpine meadow and even became later in the meadow steppe and typical steppe. In most cases, the increase in spring temperatures and precipitation promoted the greening up of herbaceous plants, while sunshine duration was positively correlated with the green-up date of herbaceous plants. For the autumn phenophases, the proportions of the earlier and later trends were very close, but the trends varied among the grassland types. The leaf coloring dates of the forages were delayed in the meadow steppe and alpine steppe but showed no distinct pattern in the typical steppe or alpine meadow and even became earlier in the desert steppe. In most cases, the increase in growing season temperature led to an earlier leaf coloring date of the herbaceous plants, but the increase in the preseason precipitation delayed the leaf coloring date. Our results suggested that the phenophases of herbaceous plants have complicated responses to multiple environmental factors, which makes predicting future phenological changes difficult.

Multi-Climate Factors and the Preceding Growth Stage of Vegetation Co-Regulated the Variation of the End of Growing Season in Northeast Inner Mongolia, China

The end of growing season (EOS) is an effective indicator of annual vegetation growth. Previous studies have revealed the dynamics of the EOS with climate change, while the influence of vegetation growth in preceding stage and peak of growing season (POS) on the EOS has not been thoroughly documented. In this study, we used four smoothing methods to obtain EOS dates from the Normalized Difference Vegetation Index (NDVI) in northeast Inner Mongolia (NIM) between 2001–2017, assessed the differences in the spatiotemporal variations of the EOS obtained by the four smoothing methods, and then investigated the impacts of climate factors, summer/ autumn vegetation growth and POS on the EOS. The results showed that the EOS dates obtained with different smoothing methods were broadly consistent in terms of their spatial patterns and temporal trends. In terms of climate factors, the EOS was driven mainly by preseason precipitation for the majority of vegetation types and advanced with increasing precipitation. For the steppe, both minimum temperature (Tmin) and relative humidity (RHU) played the most important roles in regulating the variation of EOS which was delayed with an increase in Tmin and reduction in RHU. Furthermore, our study found an earlier POS and vigorous vegetation growth in summer would jointly advance the steppe EOS, but these relationships were the opposite of each other in meadow and forest regions. Interestingly, the EOS of NIM was more related with vegetation growth in the most recent period before the EOS. This study highlights the importance of ecological processes in the preceding growth stage for understanding the dynamics of EOS.

Daily minimum temperature and precipitation control on spring phenology in arid‐mountain ecosystems in China

AbstractClimate anomaly has caused substantial shifts in phenology of mountain ecosystems, but the underlying mechanism of phenological responses to climate change is still not well understood. In essence, the abundance of vegetation communities increases the complexity of phenology‐climate relationships, leading to a certain limitation in predictions of future dynamics among different vegetation types using a unified model. In this study, we focused on the climatic constraints on spring phenology in arid mountains (AMs) of China, and emphasis was laid on accurate representation of mechanisms that control phenology across different vegetation types. We Firstly explored spatio‐temporal variations in satellite‐derived estimates of starting date of vegetation growing season (SOS) over the period 2000–2015 using moderate‐resolution imaging spectro‐radiometer (MODIS) normalized difference vegetation index (NDVI). Phenological models in response to climate variability were then established by using mixed‐effect models based on satellite observations and an extensive dataset of climatic measurements. Our results showed that the climatic regulation on SOS varied greatly over vegetation types. More climatic factors that regulate phenological development were found in grassland than forest and shrubland. At ecosystem level, two critical climate factors, daily minimum temperature (Tmin) and precipitation, explained 74–95% of total variability in predicted SOS. The observed sensitivity to Tmin is expected to be closely linked with the risk of frost damage, while preseason precipitation determines water availability in spring. The varying ecosystem sensitivity revealed the different resilience and adaptability to changing climate among vegetation types, which have been linked to their eco‐physiological characteristics (e.g., water use efficiency) and environmental conditions (e.g., elevation). Overall, our results indicate a strong dependence of spring phenology on Tmin and precipitation, and create an opportunity for a more realistic representation of vegetation phenology and growth of AM plants in China in land surface models.

Vegetation green up under the influence of daily minimum temperature and urbanization in the Yellow River Basin, China

Abstract Climate conditions are the major driving factors of vegetation phenology. However, there is limited effort to monitor dynamics of vegetation phenology and its responses to climate change and urbanization. Using NDVI data from 1982 to 2015, this study investigated the spatiotemporal change of spring green-up date (GUD) across the Yellow River Basin (YRB) and estimated the possible effects of different climatic factors on it. Additionally, the urban-rural differences in GUD and its linkage to spring land surface temperature (LST) for YRB’s major cities over 2001–2015 were investigated. The results showed that the GUD significantly advanced at a rate of 0.42 days yr−1 and delayed spatially from southeast to northwest. The interannual variations in regionally averaged GUD were driven mainly by preseason min-temperature (Tmin). Spatially, the effect of preseason Tmin was strongest in the central and western region. The confounding effects of preseason maximum temperature (Tmax) and precipitation jointly affected the GUD, while insolation had a weak impact on GUD. Moreover, the sensitivity of GUD to preseason Tmin and precipitation weakened with an increasing mean annual preseason precipitation gradient, but the sensitivity to preseason Tmax was gradually enhanced. Furthermore, the difference in the GUD between urban and rural areas presented a significant logarithmic relationship with the distance away from the urban center, and it was strongly related to the regional LST. Our findings confirmed the importance of Tmin and urbanization in regulating changes in GUD and further suggested that LST should be considered to develop an improved model of GUD under future climate change and urban development.

Divergent shifts in peak photosynthesis timing of temperate and alpine grasslands in China

The changing climate is shifting the seasonality of photosynthesis in vegetation, including the start (SOS), end (EOS), and length (LOS) of the growing season, and the peak photosynthesis timing (PPT). While the SOS, EOS, and LOS have been widely investigated, the PPT of grasslands – as a proxy for the response of seasonal plant photosynthesis to climate change – has been overlooked. In this study, we propose a hybrid generalized additive model (HGAM) method to extract PPT using the Vegetation Photosynthesis Model (VPM)-based gross primary production (GPP) product, and we examine the dynamics, drivers, and consequences of PPT changes in temperate and alpine grasslands in China over 2000–2016. We found that the PPTs in temperate and alpine grasslands have exhibited advancing (with −0.68 days yr−1, p < 0.05) and delaying (with 0.29 days yr−1, p = 0.158) trends, respectively. In addition, preseason precipitation and soil moisture were positively correlated with the PPT in temperate and alpine grasslands, respectively, while the preseason temperature consistently controlled the PPT changes in both grasslands. Furthermore, we found that an earlier PPT was associated with higher annual production in the temperate grasslands but not in the alpine grasslands in China. The divergent PPT patterns indicated the varied adaptation characteristics to climatic constraints in the temperate and alpine grasslands and also caused different consequences on carbon uptake. This study highlights the importance of PPT in understanding the spatiotemporal dynamics of vegetation photosynthesis and the carbon cycle under a changing climate.

Combined Effects of Precipitation and Temperature on the Responses of Forest Spring Phenology to Winter Snow Cover Dynamics in Northeast China

The start date of vegetation growing season (SOS) is generally considered as an essential indicator to reflect vegetation growth condition. To date, relatively little research has explored the combined effects of temperature and precipitation on the responses of forest spring phenology to snow cover in detail. To investigate this, we applied the developed plant phenology index (PPI) derived from Moderate Resolution Image Spectroradiometer (MODIS) to estimate SOS over Northeast China from 2004 to 2018, and explored the relationship between SOS and climate variables, such as temperature, precipitation and snow cover. Our results indicated that winter snow cover dynamics had a significant effect on the forest spring growth in the following year. SOS showed a negative correlation with snow cover duration (SCD) and the ending date of snow cover (SCED), whereas had a positive correlation with the onset date of snow cover (SCOD). It implied that a longer SCD, later SCED and earlier SCOD would promote forest growth. Furthermore, we first revealed that SOS was more closely associated with the preseason temperature than winter temperature. Most regions exhibited a significant positive correlation with increasing preseason temperature, but the winter temperature showed an opposite pattern except for the cool-temperate needleleaf forest region. Meanwhile, SOS had a negative relationship with precipitation, especially for preseason precipitation. Furthermore, with increasing of temperature and precipitation in winter, the responses of SOS to snow cover phenology in temperate needleleaf and broadleaf mixed-forest region are contrary to that in the other three regions. During the period from SCED to SOS, the responses of SOS to snow cover phenology varied among different vegetation zones and the gradients of temperature and precipitation.

Climate-phenology-hydrology interactions in northern high latitudes: Assessing the value of remote sensing data in catchment ecohydrological studies

We assessed the hydrological implications of climate effects on vegetation phenology in northern environments by fusion of data from remote-sensing and local catchment monitoring. Studies using satellite data have shown earlier and later dates for the start (SOS) and end of growing seasons (EOS), respectively, in the Northern Hemisphere over the last 3 decades. However, estimates of the change greatly depend on the satellite data utilized. Validation with experimental data on climate-vegetation-hydrology interactions requires long-term observations of multiple variables which are rare and usually restricted to small catchments. In this study, we used two NDVI (normalized difference vegetation index) products (at ~25 & 0.5 km spatial resolutions) to infer SOS and EOS for six northern catchments, and then investigated the likely climate impacts on phenology change and consequent effects on catchment water yield, using both assimilated data (GLDAS: global land data assimilation system) and direct catchment observations. The major findings are: (1) The assimilated air temperature compared well with catchment observations (regression slopes and R2 close to 1), whereas underestimations of summer rainstorms resulted in overall underestimations of precipitation (regression slopes of 0.3–0.7, R2 ≥ 0.46). (2) The two NDVI products inferred different vegetation phenology characteristics. (3) Increased mean pre-season temperature significantly influenced the advance of SOS and delay of EOS. The precipitation influence was weaker, but delayed SOS corresponding to increased pre-season precipitation at most sites can be related to later snow melting. (4) Decreased catchment streamflow over the last 15 years could be related to the advance in SOS and extension of growing seasons. Greater streamflow reductions in the cold sites than the warm ones imply stronger climate warming impacts on vegetation and hydrology in colder northerly environments. The methods used in this study have potential for better understanding interactions between vegetation, climate and hydrology in observation-scarce regions.

Slowdown of spring green-up advancements in boreal forests

There is a consensus that the spring phenology of deciduous forests is advancing in response to global warming. Since the late 1990s, however, this tendency of spring phenology advancement has been weakened in over 60% of boreal forests, particularly in Siberia (−0.58 day yr−1 for 1982–1997 vs. −0.17 day yr−1 for 1982–2013) and northwestern North America (NWNA; −0.42 day yr−1 for 1982–1997 vs. 0.07 day yr−1 for 1982–2013). This study investigated the major factor in the weakening trends in the advancement of the start of the growing season (SOS) based on the satellite-observed normalized difference vegetation index (NDVI) in two regions by quantifying the effects of four climatic fields—winter duration (WD; the number of freezing days), pre-season temperature (PT; accumulated temperature from late winter to early spring), green-up temperature (GT; accumulated temperature around the green-up date), and pre-season precipitation (PR; accumulated precipitation before the green-up date)—on changes in the spring green-up trend. The GT explained the majority of the slowdown in the SOS trends in recent decades. In Siberia, the GT increases contributed to the advancement of the SOS during the 1980s and 1990s; however, the GT increase reduced to less than half of these periods resulting in a slowdown of the SOS advancing trend since the early 2000s. In NWNA, GT increases and WD shortening drove the SOS advancement until the late 1990s; however, both effects have been diminished to near zero to result in no further SOS advancements. This study demonstrates that the recent slowdown of the SOS advancing trends over Siberia and NWNA was largely attributed to the weakening of the warming trends, rather than the sensitivity changes of spring phenology to climate variables. This study suggests that the natural climate variability strongly affects the decadal variations in the boreal forest spring phenology.

Climate and Spring Phenology Effects on Autumn Phenology in the Greater Khingan Mountains, Northeastern China

Vegetation phenology plays a key role in terrestrial ecosystem nutrient and carbon cycles and is sensitive to global climate change. Compared with spring phenology, which has been well studied, autumn phenology is still poorly understood. In this study, we estimated the date of the end of the growing season (EOS) across the Greater Khingan Mountains, China, from 1982 to 2015 based on the Global Inventory Modeling and Mapping Studies (GIMMS) normalized difference vegetation index third-generation (NDVI3g) dataset. The temporal correlations between EOS and climatic factors (e.g., preseason temperature, preseason precipitation), as well as the correlation between autumn and spring phenology, were investigated using partial correlation analysis. Results showed that more than 94% of the pixels in the Greater Khingan Mountains exhibited a delayed EOS trend, with an average rate of 0.23 days/y. Increased preseason temperature resulted in earlier EOS in most of our study area, except for the semi-arid grassland region in the south, where preseason warming generally delayed EOS. Similarly, EOS in most of the mountain deciduous coniferous forest, forest grassland, and mountain grassland forest regions was earlier associated with increased preseason precipitation, but for the semi-arid grassland region, increased precipitation during the preseason mainly led to delayed EOS. However, the effect of preseason precipitation on EOS in most of the Greater Khingan Mountains was stronger than that of preseason temperature. In addition to the climatic effects on EOS, we also found an influence of spring phenology on EOS. An earlier SOS led to a delayed EOS in most of the study area, while in the southern of mountain deciduous coniferous forest region and northern of semi-arid grassland region, an earlier SOS was often followed by an earlier EOS. These findings suggest that both climatic factors and spring phenology should be incorporated into autumn phenology models in order to improve prediction accuracy under present and future climate change scenarios.

Observed and Simulated Sensitivities of Spring Greenup to Preseason Climate in Northern Temperate and Boreal Regions

AbstractVegetation phenology plays an important role in regulating land‐atmosphere energy, water, and trace‐gas exchanges. Changes in spring greenup (SG) have been documented in the past half‐century in response to ongoing climate change. We use normalized difference vegetation index generated from NOAA's advanced very high resolution radiometer data in the Global Inventory Modeling and Monitoring Study project over the 1982–2005 period, coupled with climate reanalysis (Climate Research Unit‐National Centers for Environmental Prediction) to investigate the SG responses to preseason climate change in northern temperate and boreal regions. We compared these observed responses to the simulated SG responses to preseason climate inferred from the Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) over 1982–2005. The observationally inferred SG suggests that there has been an advance of about 1 days per decade between 1982 and 2005 in the northern midlatitude to high latitude, with significant spatial heterogeneity. The spatial heterogeneity of the SG advance results from heterogeneity in the change of the preseason climate as well as varied vegetation responses to the preseason climate across biomes. The SG to preseason temperature sensitivity is highest in forests other than deciduous needleleaf forests, followed by temperate grasslands and woody savannas. The SG in deciduous needleleaf forests, open shrublands, and tundra is relatively insensitive to preseason temperature. Although the extent of regions where the SG is sensitive to preseason precipitation is smaller than the extent of regions where the SG is sensitive to preseason temperature, the biomes that are more sensitive to temperature are also more sensitive to precipitation, suggesting the interactive control of temperature and precipitation. In the mean, the CMIP5 ESMs reproduced the dominant latitudinal preseason climate trends and SG advances. However, large biases in individual ESMs for the preseason period, climate, and SG sensitivity imply needed model improvements to climate prediction and phenological process parameterizations.

Effect of climate change on vegetation phenology of different land-cover types on the Tibetan Plateau

ABSTRACTResearch in vegetation phenology change has been one heated topic of current ecological and climate change study. The Tibetan Plateau, as the highest plateau of the earth, is more vulnerable and sensitive to climate change than many other regions. In this region, shifts in vegetation phenology have been intensively studied during recent decades, primarily based on satellite-retrieved data. In this study, we explored the spatiotemporal changes of vegetation phenology for different land-cover types in the Tibetan Plateau and characterized their relationship with temperature and precipitation by using long-term time-series datasets of normalized difference vegetation index (NDVI) from 1982 to 2014. Diverse phenological changes were observed for different land-cover types, with an advancing start of growing season (SOS), delaying end of growing season (EOS) and increasing length of growing season (LOS) in the eastern Tibetan Plateau where meadow was the dominant vegetation type, but with the opposite changes in the steppe and sparse herbaceous or sparse shrub regions which are mostly located in the northwestern and western edges of the Tibetan Plateau. Correlation analysis indicated that sufficient preseason precipitation may delay the SOS of evergreen forests in the southeastern Plateau and advance the SOS of steppe and sparse herbaceous or sparse shrub in relatively arid areas, while the advance of SOS in meadow areas could be related to higher preseason temperature. For EOS, because it is less sensitive to climate change than SOS, the response of EOS for different land-cover types to precipitation and temperature were more complicated across the Tibetan Plateau.

Phenological response of different vegetation types to temperature and precipitation variations in northern China during 1982–2012

ABSTRACTPlant phenology is influenced by various climatic factors such as temperature, precipitation, insolation, and humidity, etc. Among these factors, temperature and precipitation are proved to be the most important. However, the relative importance of these two factors is different among various phenophases and regions and is seldom discussed along environmental gradients. Based on normalized difference vegetation index (NDVI) data from the NDVI3g dataset and using the mid-point method, we extracted the start date of the growing season (SOG) and the end date of the growing season (EOG) in northern China during 1982–2012. To determine which climate factor was more influential on plant phenology, partial correlation analysis was applied to analyse the spatial difference between the response of SOG and EOG to temperature and precipitation. Finally, we calculated the temperature and precipitation sensitivities of the SOG and EOG. The results showed that: (1) SOG displayed an advancing trend in most regions, while EOG was delayed for all the vegetation types during 1982–2012. (2) SOG was mainly triggered by preseason temperature. The increase in temperature caused an overall advance in SOG. However, the relationship between SOG and precipitation varied among different vegetation types. Regarding EOG, precipitation had greater impacts than temperature in relatively arid environments, such as deserts, steppes and meadow biomes. (3) The response of vegetation phenology (both SOG and EOG) to temperature became stronger with increasing preseason precipitation across space. The response of EOG to precipitation became weaker from arid regions to relatively humid regions. These results provide a better understanding of the spatial pattern of the phenological response along the precipitation gradient and a reference for assessing impacts of future climate change on vegetation phenology, especially in transitional and fragile zones.

Divergent shifts and responses of plant autumn phenology to climate change on the Qinghai-Tibetan Plateau

Autumn phenology along with spring/summer phenology controls the length of the vegetation growing season and significantly influences ecosystem biogeochemical cycles. Many previous studies have focused on spring/summer phenology. However, fewer studies have addressed autumn phenology because of no available or insufficient observations. Based on a series of long-term and continuous observations of autumn phenological events (8000+ records) on the Qinghai-Tibetan Plateau (QTP), we made a comprehensive assessment of autumn phenological shifts and their responses to climate change during the period from 1981 to 2011. Although a significantly delayed overall trend in autumn phenology was observed across the QTP from 1981 to 2011, the autumn phenologies showed divergent shifting trends and responses to climate change among plant species, phenological events, study periods and thermal conditions. Larger variations were observed for the occurrence dates of fruit-related events than foliar events. Significantly advanced shifts in autumn phenology were observed for woody plants (mostly owing to fruit-related phenological events), while significantly delayed shifts were observed for herbaceous plants (mostly owing to foliar events). The autumn phenology of woody plants varied little among plant species, recording periods and thermal conditions but varied greatly under different temperature change trends. The autumn phenology of herbaceous plants varied greatly among plant species, recording periods, thermal conditions and sites with different temperature change trends. The occurrence dates of most phenological events for herbaceous plants were positively correlated with the preseason temperature and negatively correlated with the preseason precipitation, while opposite relationships were observed for woody plants. Our results provide new field evidence for the dispersive changes in autumn phenology on the QTP and suggest that the dispersive shifts in autumn phenology and their different responses to climate warming should be considered when assessing the impacts of climate change on vegetation dynamics and ecosystem biogeochemical cycles.

Trends and climatic sensitivities of vegetation phenology in semiarid and arid ecosystems in the US Great Basin during 1982–2011

Abstract. We quantified the temporal trend and climatic sensitivity of vegetation phenology in dryland ecosystems in the US Great Basin during 1982–2011. Our results indicated that vegetation greenness in the Great Basin increased significantly during the study period, and this positive trend occurred in autumn but not in spring and summer. Spatially, increases in vegetation greenness were more apparent in the northwestern, southeastern, and eastern Great Basin but less apparent in the central and southwestern Great Basin. In addition, the start of growing season (SOS) was not advanced while the end of growing season (EOS) was delayed significantly at a rate of 3.0 days per decade during the study period. The significant delay in EOS and lack of earlier leaf onset caused growing season length (GSL) to increase at a rate of 3.0 days per decade. Interestingly, we found that the interannual variation of mean vegetation greenness calculated for the period of March to November (spring, summer, and autumn – SSA) was not significantly correlated with mean surface air temperature in SSA but was strongly correlated with total precipitation. On a seasonal basis, the variation of mean vegetation greenness in spring, summer, and autumn was mainly attributable to changes in pre-season precipitation in winter and spring. Nevertheless, climate warming appeared to play a strong role in extending GSL that, in turn, resulted in the upward trend in mean vegetation greenness. Overall, our results suggest that changes in wintertime and springtime precipitation played a stronger role than temperature in affecting the interannual variability of vegetation greenness, while climate warming was mainly responsible for the upward trend in vegetation greenness we observed in Great Basin dryland ecosystems during the 30-year period from 1982 to 2011.

Precipitation impacts on vegetation spring phenology on the Tibetan Plateau.

The ongoing changes in vegetation spring phenology in temperate/cold regions are widely attributed to temperature. However, in arid/semiarid ecosystems, the correlation between spring temperature and phenology is much less clear. We test the hypothesis that precipitation plays an important role in the temperature dependency of phenology in arid/semiarid regions. We therefore investigated the influence of preseason precipitation on satellite-derived estimates of starting date of vegetation growing season (SOS) across the Tibetan Plateau (TP). We observed two clear patterns linking precipitation to SOS. First, SOS is more sensitive to interannual variations in preseason precipitation in more arid than in wetter areas. Spatially, an increase in long-term averaged preseason precipitation of 10mm corresponds to a decrease in the precipitation sensitivity of SOS by about 0.01daymm(-1) . Second, SOS is more sensitive to variations in preseason temperature in wetter than in dryer areas of the plateau. A spatial increase in precipitation of 10mm corresponds to an increase in temperature sensitivity of SOS of 0.25day°C(-1) (0.25 day SOS advance per 1°C temperature increase). Those two patterns indicate both direct and indirect impacts of precipitation on SOS on TP. This study suggests a balance between maximizing benefit from the limiting climatic resource and minimizing the risk imposed by other factors. In wetter areas, the lower risk of drought allows greater temperature sensitivity of SOS to maximize the thermal benefit, which is further supported by the weaker interannual partial correlation between growing degree days and preseason precipitation. In more arid areas, maximizing the benefit of water requires greater sensitivity of SOS to precipitation, with reduced sensitivity to temperature. This study highlights the impacts of precipitation on SOS in a large cold and arid/semiarid region and suggests that influences of water should be included in SOS module of terrestrial ecosystem models for drylands.

Influences of temperature and precipitation before the growing season on spring phenology in grasslands of the central and eastern Qinghai-Tibetan Plateau

Spatial variations in phenological responses to temperature have not been reported for grasslands of the Qinghai-Tibetan Plateau. Using satellite-derived normalized difference vegetation index and meteorological records from 1982 to 2006, we characterized the spatial patterns of grassland green-up onset in relation to air temperature and precipitation before the growing season (“preseason” henceforth) in the central and eastern plateau by combining linear programming with correlation analysis. Green-up onset near half of the meteorological stations was significantly correlated (p<0.10) with precipitation and thermal spring onset (TSO) date based on the cumulative temperature less than 6 weeks before the onset. The green-up onset paralleled the advance in TSO in the southwestern, southeastern, eastern, and northeastern parts of the plateau. The TSO and preseason precipitation (PPT) explained part of the inter-annual phenological variations, with r2 varying between 0.05 and 0.55 and averaging 0.28, and did not explain delay of green-up onset in some areas. Increasing preseason temperature tended to advance green-up onset in relatively moist areas. PPT exerted a stronger influence on green-up onset in drier areas. These results indicate spatial differences in the key environmental influences on spring phenology. To improve the ability to predict onset, ground-based community-level phenological studies and spatial scaling-up of the phenology–climate relationship will be necessary.

Preseason precipitation probabilities as an aid to corn planting decisions

An analysis of corn yield data from 5 countries and precipitation data from 5 representative locations in eastern Nebraska from a 58-year period 1925–1983 show that yields are above normal when the preseason season precipitation (1 September–15 May) is above average. Long term precipitation records of 80 or more years were used to determine the probability, at different times during a 75-day period prior to planting, that the preseason precipitation at planting time would be average or higher.

Climatic Change, Weather Variability, and Corn Production1

AbstractA crop/weather model was used to determine the impact of changes in climate and weather variability on corn (Zea mays L.) production from 1891 to 1983. Five Corn Belt states, Illinois, Indiana, Iowa, Missouri, and Ohio, were included in the study. These states produce over 50% of the U.S. corn crop. A cooling trend from 1930 to 1972 was accompanied by increasing rainfall in July and August, and by decreasing weather variability. These three factors were favorable for corn yield increase. Simulated corn yields, calculated from weather data, increased 970 kg ha−1 from 1930 to 1972 because of improved weather for corn. After 1972 there was greater weather variability and higher intensity rainfall events. Fertilizer use on corn increased substantially in the 1960s and increased at slower rate after 1972. The annual increase in corn yield with normal weather after 1972 was less than half as much as it was from 1960 to 1972. Highest yields of corn have been associated with normal preseason precipitation, normal June temperature, below normal temperature in July and August, and above normal rainfall in July and August. The period after 1970 was expected to warm but weather variability has masked the identification of a trend.

Association of Weather Variables with Genotype × Environment Interactions in Grain Sorghum1

The objective of this study was to determine the relative contribution of several weather variables during various plant growth stages to variation in environment and genotype ✕ environment (GE) interactions of grain sorghum [Sorghum bicolor (L.) Moench] genotypes in different maturity groups. Three growth stages viz., planting to panicle initiation (GS1), panicle initiation to anthesis (GS2), and anthesis to physiological maturity (GS3), were approximated with three periods of crop season, each with an equal number of growing degree days. Variation in temperature and rainfall accounted for more than half of the environment and genotype ✕ environment interaction sums of squares for yield, and seed number and seed weight components of yield. However, the extent to which these variables contributed to differential genotypic response to environments varied among maturity groups and growth stages. Temperature was the most important factor affecting environmental variability for yield and seed number. Effects of temperature and rainfall in GS2 and GS3 were highly associated with GE interaction effects for yield in all maturity groups. Generally, minimum temperature was more important than maximum temperature especially for the early and the late maturing genotypes. Preseason precipitation contributed more than seasonal rainfall to the GE interaction sums of square for yield and seed number, however, the opposite was observed for seed weight. Variation in weather factors contributed more to GE interaction for yield of the late maturing genotypes than the early and medium maturing genotypes. More information on environmental factors is needed to better understand the nature of GE interaction in grain sorghum.