Seasonal Rainfall Time Research Articles

Climate-Exacerbated Impacts May Drive Maladaptive Action in Agriculture

Abstract In the eastern Corn Belt of the United States, climate change is projected to bring warmer and wetter conditions, with more variability in the seasonal timing of rainfall, creating a multitude of challenges for agricultural production. While there are multiple adaptations to reduce the vulnerability of production to a changing climate, these adaptations have varying implications for other ecosystem services such as soil health, carbon sequestration, and water quality. We explore how beliefs about and experiences with climate change might influence adaptations that vary in their provisioning of a variety of ecosystem services, and how these adaptations may vary by characteristics of the farm and farmer. Survey data were collected from 908 respondents from August through October 2019. We find only one proposed adaptation, additional tile drainage, is associated with self-reported prior negative experiences with climate change and concern about future impacts. The other proposed adaptations (i.e., cover crops, filter strips, additional fertilizer) are associated with farmer identity. The type of farmer who is likely to adapt is generally reminiscent of the type who engage in conservation practices: younger, more educated, with off-farm income and larger farms. Our results indicate that many proposed adaptations are not perceived as effective ways to mitigate specific climate-driven impacts. However, increasing tile drainage is perceived as such, and there may be a need to offset the potential negative impacts to water quality of this likely adaptation through the promotion of edge-of-field filtration practices. Significance Statement The purpose of this study is to better understand how beliefs about and experiences with climate change may influence adaptations that vary in their provisioning of a suite of ecosystem services. We find that those who are adapting directly to the most severe and frequent climate-exacerbated impact, heavy rain at the wrong time of year, are likely to adapt in ways that may benefit production (e.g., increasing drainage tile to ensure fields are not inundated by spring rains) but have negative feedback to society in terms of water quality. Most proposed adaptations are not perceived as effective means of increasing resilience to experienced impacts but rather as practices that are the norm among conservation-minded farmers with larger operations.

Delayed wet season increases soil net N mineralization in a seasonally dry tropical forest

Seasonal precipitation regime plays a vital role in regulating nutrient dynamics in seasonally dry tropical forests. Present evidence suggests that not only wet season precipitation is increasing in the tropics of South China, but also that the wet season is occurring later. However, it is unclear how nutrient dynamics will respond to the projected precipitation regime changes. We assessed the impacts of altered seasonal precipitation on soil net N mineralization in a secondary tropical forest. Since 2013, by reducing throughfall and/or irrigating experimental plots, we delayed the wet season by two months from April–September to June–November (DW treatment) or increased annual precipitation by 25% in July and August (WW treatment). We measured soil net N mineralization rates and assessed soil microbial communities in January, April, August and November in 2015 and 2017. We found that a wetter wet season did not significantly affect soil microbes or net N mineralization rates, even in the mid-wet season (August) when soil water content in the WW treatment increased significantly. By contrast, a delayed wet season enhanced soil microbial biomass and altered microbial community structure, resulting in a two-fold increase in net N mineralization rates relative to controls in the early dry season (November). Structural equation modeling showed that the changes in net N mineralization during the early dry season were associated with altered soil microbial communities, dissolved organic N, and litterfall, which were all affected by enhanced soil water content. Our findings suggest that a delayed wet season could have a greater impact on N dynamics than increased precipitation during the wet season. Changes in the seasonal timing of rainfall might therefore influence the functioning of seasonally dry tropical forests.

Understanding the Representativeness of Tree Rings and Their Carbon Isotopes in Characterizing the Climate Signal of Tajikistan

The juniper tree forest is a critical component of the carbon, water, and energy cycles of Tajikistan. However, to date, long-term information about tree-ring isotopes is limited in this region. Here, we developed tree-ring width (TRW) and tree-ring 13C chronologies for juniper trees (Juniperus seravschanica (Juniperus excelsa subsp.polycarpos (K. Koch) Takht.) and Juniperus turkestanica (Juniperus pseudosabina Fisch. & C. A. Mey)) and investigated their dendroclimatic signals in the northwest of the Pamir-Alay (NWPA) mountains in Tajikistan. Tree-ring ∆13C and TRW of juniper presented different sensitivities to monthly precipitation. Moreover, ∆13C in juniper showed consistently significant relationships with climatic factors in larger seasonal windows than TRW did. Dendroclimatological analysis demonstrates that precipitation has significant effects on tree growth and isotope enrichment. Late summer to early winter temperature is one limiting factor for the TRW chronologies, but previous spring, summer, and autumn temperature and precipitation from the previous July to the current May were the dominant climatic factors accounting for inter-annual variations in the ∆13C chronologies. This verified that the multi tree-ring parameters of juniper in Tajikistan are a promising tool for investigating inter-annual climate variations. Furthermore, the stable carbon isotopes of tree rings have proven to be powerful evidence of climatic signals. The moisture-sensitive tree-ring isotope provides opportunities for complex investigations of changes in atmospheric circulation patterns and timing of seasonal rainfall. Our results highlight the need for more detailed studies of tree growth responses to changing climate and tree-ring isotopes to understand source water variations (especially baseflow) of the juniper tree forest.

Projected Changes in Intra-Season Rainfall Characteristics in the Niger River Basin, West Africa

The magnitude and timing of seasonal rainfall is vitally important to the health and vitality of key agro-ecological and social-economic systems of the Niger River Basin. Given this unique context, knowledge concerning how climate change is likely to impact future rainfall characteristics and patterns is critically needed for adaptation and mitigation planning. Using nine ensemble bias-corrected climate model projection results under RCP4.5 and RCP8.5 (RCP—Representative Concentration Pathway) emissions scenarios at the mid-future time period, 2021/2025-2050 from the Coordinated Regional Climate Downscaling Experiments (CORDEX) dataset; this study provides a comprehensive analysis of the projected changes in rainfall characteristics in three agro-ecological zones of the Niger River Basin. The results show an increase in the average rainfall of about 5%, 10–20% and 10–15% for the Southern Guinea, Northern Guinea and Sahelian zones, respectively, relative to the baseline, 1981/1985–2005. On the other hand, the change in future rainfall intensities are largely significant and the frequency of rainfall at the low, heavy and extreme rainfall events in the future decrease at most locations in the Niger River Basin. The results also showed an increase in the frequency of moderate rainfall events at all locations in the basin. However, in the Northern Guinea and Sahel locations, there is an increase in the frequency of projected heavy and extreme rainfall events. The results reveal a shift in the future onset/cessation and a shortening of the duration of the rainy season in the basin. Specifically, the mean date of rainfall onset will be delayed by between 10 and 32 days. The mean onset of cessation will also be delayed by between 10 and 21 days. It is posited that the projected rainfall changes pose serious risks for food security of the region and may require changes in the cropping patterns and management.

A Shift in Seasonal Rainfall Reduces Soil Organic Carbon Storage in a Cold Desert

Shifts in the seasonal timing of rainfall have the potential to substantially affect the immense terrestrial stores of soil organic carbon (C, SOC). It remains unclear, however, how changes in the timing of rainfall are influencing SOC storage. We hypothesized that a sustained shift in rainfall timing from winter to a spring-summer regime would reduce desert SOC stores by creating moist and warm soil conditions, thus promoting decomposition. To investigate this, we evaluated how an 11-year seasonal shift in rainfall (winter to springsummer regime) affected SOC storage (that is, dissolved organic C, light SOC, and heavy SOC) in soils beneath dominant shrub and perennial grass species in a cold desert sagebrush-steppe ecosystem. We also measured the soil C to nitrogen (N) ratios, standing litter stocks, and root biomass C to help interpret the long-term changes in SOC stores. As predicted, a seasonal shift in rainfall caused heavy SOC to decline beneath Artemisia tridentata ssp. wyomingensis by 14%, from 3.1 to 2.7 kg C m -2 , and Pseudoroegneria spicata by 19%, from 3.0 to 2.4 kg C m -2 . Neither dissolved organic C, nor the light fraction, responded to changes in rainfall. The C to N ratio of heavy SOC beneath Artemisia declined by at least 6% under the warmer and moister conditions of the spring-summer regime, suggesting that alterations in decomposition dynamics contributed to the loss of SOC. Unexpectedly, coarse litter and root C in Artemisia soils were lower under the spring-summer than winter rainfall regime, suggesting that a decline in litter inputs may also have contributed to the loss of SOC. The C to N ratio of heavy SOC, litter stores (that is, coarse litter and thatch), and root C in Pseudoroegneria soils demonstrated similar responses as in Artemisia soils, but these variables were at best only marginally significant. Our results suggest that a sustained seasonal shift in rainfall from winter to spring-summer will reduce heavy SOC across cold deserts, and that this reduction will stem from alterations in decomposition dynamics and net primary production by plants. Further, as global temperatures rise we may see more overlap of moist and warm soil conditions, especially in ecosystems with winter rainfall regimes (for example, Mediterranean-climate ecosystems and temperate forests), that may reduce SOC in the absence of rainfall changes.

Cotton farmers’ vulnerability to climate change in Gokwe District (Zimbabwe): impact and influencing factors

This study analyzes the vulnerability of cotton farmers to climate change in a cotton growing district in Zimbabwe. The vulnerability indicators studied include cotton output and farmers’ livelihoods from cotton farming. In order to examine climate variability and change, a time series analysis of two variables: temperature and rainfall was done for a period of 30 years, resulting in graphs of any climate anomalies. Correlation tests between the independent variable (the climate) and the dependent variable (cotton output) were assessed in order to examine the nature and the magnitude of the relationship between the two. The opinions of 100 randomly sampled farmers were analysed in an attempt to verify the climate scenarios and cotton production trends, as well as to understand their adaptation to climate change. Negative rainfall deviations from the long-term mean and positive temperature deviations dominated the climate trend scenarios’ results. Cotton production levels declined as precipitation decreased and temperatures increased across the district. The survey revealed that a significant number of farmers believed that temperatures were increasing and precipitation was declining. Farmers’ perceptions on whether the climate was changing were greatly influenced by incidences of drought and changes in the seasonal timing of rainfall, and in few cases unusual floods. The majority believed the frequency of droughts was increasing. While farmers were prepared to adapt to changes in climate, their options were very limited. The results show that farmers are highly vulnerable to climate change and that there is a need to invest in climate adaptation strategies, including policies on irrigation and early warning systems to help farmers to cope better and to reduce their vulnerability to climate change.

Genetic diversity does not affect the invasiveness of fountain grass (Pennisetum setaceum) in Arizona, California and Hawaii

ABSTRACT Pennisetum setaceum (Poaceae) is a perennial bunch grass that invaded the United States during the 20th century and is highly invasive in Hawaii, moderately invasive in Arizona, and not yet invasive in southern California. Pennisetum setaceum is apomictic, a condition that is normally associated with low genetic variation within populations, but even moderate levels of genetic variation among populations could account for differences in invasiveness. To determine whether genetic factors are causing the variable invasion success, we used Inter‐Simple Sequence Repeat markers (ISSRs) to examine genetic variation in populations from the three areas. Screening of 16 primers revealed no genetic variation within any population or between any geographical areas, a pattern consistent with complete apomixis. Variation in invasion success appears unrelated to genetic differences among populations. Differences in the seasonal timing of rainfall among the regions may be the cause of variable invasiveness of fountain grass. Alternatively, differences in timing of introduction or duration of lag phase may have limited invasiveness in Arizona and southern California.

Patterns of seed germination in Californian serpentine grassland species.

Germination of nine Californian serpentine annual species and one perennial grass was examined as a function of soil and litter cover and seasonal timing of rainfall. Germination responses varied with the date of moisture application, and the patterns of variation differed among species. Germination occurred in waves over time, but in most of the species, virtually all the seeds had germinated by December. These results indicate that yearly climatic variation can affect species composition and competitive relationships among species through the germination process. Soil and litter cover produced little or no effect except for the smallest-seeded species.