Magnitude Of Rain Research Articles

Partitioning of Rainfall and Sprinkler-Irrigation by Crop Canopies: A Global Review and Evaluation of Available Research

The role of crop canopies in the global water cycle is a topic of increasing international interest. How much rain and sprinkler-irrigation water are returned to the atmosphere or reach the soils beneath crop canopies, and the pathways of those water inputs at the soil, are linked to agricultural productivity and sustainability. This concise-format review synthesized and evaluated the available, limited, observational data (138 studies) on cropland throughfall, stemflow, and/or interception for >60 crop species covering all major climate types to obtain a global analysis of rainfall and sprinkler-irrigation partitioning by crop canopies. Partitions normalized per unit rain/sprinkler-irrigation (relative fractions, %) vary greatly across crop types with the interquartile range of throughfall, stemflow, and interception being 58–83%, 2–26%, and 11–32%, respectively. Stemflow data distribution across crop types is more often different than for throughfall and interception, contributing to overall variations in the partitioning of rain and irrigation observed to date. Partitions per storm also differ depending on the magnitude of rain or sprinkler-irrigation events and the stage of crop growth. Furthermore, throughfall and stemflow input patterns at the soil surface and subsurface may erode soils through different physical processes (i.e., throughfall droplet impact/splash versus scouring by stemflow); however, more research is needed to elucidate the underlying mechanisms and overall impacts. Finally, comparative analyses of partitions among croplands, shrublands, and forests indicate that crop canopies partition rain inputs differently and that there is a lack of studies in croplands. Hence, we suggest that future effort should be directed to the partitioning of rainfall and sprinkler-irrigation by canopies in agricultural settings.

Assessment of 7Be content in precipitation in a South American semi-arid environment

There are two naturally occurring radiogenic isotopes of beryllium, 7Be and 10Be. These are produced when cosmic radiation interacts with oxygen and nitrogen in the atmosphere. After production, these radionuclides are input to ecosystems through wet and dry deposition. In recent years 7Be and 10Be have proved to be powerful tools for studying dynamic processes that occur on the surface of the earth. We measured the 7Be content in precipitation at a semiarid location in central Argentina. From November 2006 to March 2009, 68 precipitation events were collected. Measured 7Be content ranged from 0.7±0.4BqL−1 to 3.2±0.7BqL−1, with a mean of 1.7BqL−1±0.6BqL−1. Beryllium-7 content of rainfall did not show clear relationships with amount of rainfall (mm), mean intensity (mmh−1) or duration (h−1), or elapsed time between events (day). The general results indicate that for the typical range of precipitation there was no atmospheric washout and that the reload of the atmosphere is not a relevant factor, but when the amount of precipitation is very high washout may occur. On the other hand, when the 7Be content was measured during single rain events, a high content of this radionuclide was found to be associated with very low rainfall intensity (≈3mmh−1), this suggests that rain intensity could affect the 7Be content. Using all data, a good linear relationship between 7Be deposition and rain magnitude was obtained (r2=0.82, p<0.0001). Because of this, the slope of this linear regression equation may be applied as a tool for tracing environmental processes that affect the surface of the earth. We can do this by directly estimating erosion/sedimentation processes using 7Be or by estimating the input of 10Be in the environment with the aim to evaluate land degradation phenomena.

Simulation in order to choose a fitting method for extreme rainfall data

It is possible to estimate the relationship between rain magnitude and frequency of occurence by observing maximum annual data with the parametric methods of fitting any of various theorical distributions or with the nonparametric method which does not require a distributional assumption. In this article through some simulations, five methods are considered. The nonparametric method of Adamowski using the kernel function always gives an ideal distribution, but it is not possible to extrapolate the rainfall values of large return-periods. The comparison of the methods by simulation shows the clear superiority of the nonparametric method of Villasenor to estimate rainfall fields.

Effect of antecedent rainfall on runoff during low-intensity rainfall

The objective of this study was to determine the relative significance of several rainfall characteristics to the occurrence and magnitude of runoff from small (< 300 ha) watersheds during very low-intensity rainstorms (maximum rainfall intensities < 15 mm/hr). This was done by making hourly measurements of rainfall and runoff at 1-hr intervals for four years on five watersheds in western Oregon, U.S.A., an area with a modified marine climate. Normal annual precipitation at the site is 1.02m and occurs primarily as rain during the winter months. Rainfall intensities only rarely exceed 15 mm/hr. The watersheds (0.46 to 285 ha in size) were fall-planted (November) to wheat. The soils are predominantly Willakenzie series (Ultic Haploxeralfs, fine-silty, mixed, mesic). Rainfall characteristics were computed for each rainfall event, defined as a period of consecutive rainy hours separated by six or more consecutive dry hours. Included were magnitude, average intensity, maximum intensity and duration of rainfall during rainfall events, magnitude of rain during the 12, 48 and 120 hrs preceding events, the magnitude of rain since October 1 of each year and number of dry hours preceding the event. The amount of runoff was computed for each rainfall event. Stepwise discriminant analysis was used to determine those values and combinations of rainfall-event characteristics that were significant in predicting the occurrence and amount of runoff. Between 44% and 93% of the rainfall events caused no measurable runoff. Discriminant analysis indicated that the magnitude of rainfall during the 12 and 120 hrs preceding the events was more significant in determining the occurrence of runoff than either rainfall magnitude, average intensity or maximum intensity. The majority of rainfall events on all of the watersheds resulted in < 25% runoff. Discriminant analysis indicated that the amount of runoff during events was determined more by the magnitude of rainfall in the 12, 48 and 120 hrs preceding the events than by the other event characteristics. The results suggest that in climates characterized by low-intensity rainfall, antecedent rainfall is more important in controlling the occurrence and amount of runoff than rainfall magnitude or intensity. The results also suggest that more accurate predictions of runoff can be achieved by using values of antecedent-rainfall characteristics.