Average Precipitation Intensity Research Articles

Canopy interception by a spruce forest in the upper reach of Heihe River basin, Northwestern China

AbstractThe aim of this study is to understand the canopy interception of Qinghai spruce forest under conditions of different precipitation characteristics and canopy structures in the upper reach of Heihe River basin, northwestern China. On the basis of a continuous record covering our investigating period by an automatic throughfall‐collecting system, we analysed the relationships between the canopy interception and the precipitation characteristics. Our results support the well‐established exponential decay relationship between the gross precipitation and the interception percentage after the canopy is saturated. But our results sufficiently illustrate a notable point that the variations in the interception percentage are almost independent from the variations in the gross precipitation before the canopy is saturated. Our examination into the relationship between the interception and the 10‐min average intensity of precipitation demonstrates a divergent relationship, and the divergent relationship is bracketed by an upper ‘dry line’ indicating that 100% of gross precipitation was intercepted before saturation and by a lower ‘wet line’ suggesting that the actual canopy storage capacity reached the maximum and evaporation was the only component of the interception. To search for the relationship between canopy structures and interception, we grouped the canopy covers over the 90 throughfall‐collecting tanks into ten categories ranging from 0 (no cover) to 0.9 (nearly completely covered), and the corresponding canopy interception was calculated by subtracting the averaged throughfall of each canopy‐cover category from the gross precipitation. The results show that the interception percentage increases faster with increasing canopy cover under intermediate rainfall conditions than that under heavy rainfall conditions. Unexpectedly, under light rainfall conditions the increasing rate of interception percentage with increasing canopy cover and also with increasing plant area index is not faster than that under the intermediate rainfall conditions simply because the tank‐measured percentage of interception was extremely high at near‐zero canopy cover conditions. Copyright © 2013 John Wiley & Sons, Ltd.

Seasonality of Vertical Structure in Radar-Observed Precipitation over Southern Switzerland

Abstract Operational radar data reveal that precipitation systems occurring on the southern side of the Alps near Locarno, Switzerland, follow seasonal patterns of vertical reflectivity structure. Storms occurring in summer are more convective than winter season storms as indicated by more frequent observation of reflectivity at higher altitudes during summer. Individual precipitation events occurring year-round are classified by comparison to average seasonal vertical reflectivity structure. Seasonal classification of individual storms reveals a transition between winter- and summer-type storms during spring and fall that follows changes in average daily surface temperature. In addition to distinct vertical structure, summer- and winter-type storms have differences in duration, intensity, and interval between storms. Although summer- and winter-type storms result in a similar amount of total precipitation, summer-type storms have shorter duration, and therefore greater intensity. The dependence of storm types on temperature has implications for intensification of the hydrologic cycle due to climate change. Warmer winter, spring, or fall surface temperatures may affect average precipitation intensity by increasing the number of days per year that experience more intense convective precipitation while decreasing the probability of less intense stratiform precipitation.

Extreme climate, not extreme weather: the summer of 1816 in Geneva, Switzerland

Abstract. We analyze weather and climate during the "Year without Summer" 1816 using sub-daily data from Geneva, Switzerland, representing one of the climatically most severely affected regions. The record includes twice daily measurements and observations of air temperature, pressure, cloud cover, wind speed, and wind direction as well as daily measurements of precipitation. Comparing 1816 to a contemporary reference period (1799–1821) reveals that the coldness of the summer of 1816 was most prominent in the afternoon, with a shift of the entire distribution function of temperature anomalies by 3–4 °C. Early morning temperature anomalies show a smaller change for the mean, a significant decrease in the variability, and no changes in negative extremes. Analyzing cloudy and cloud-free conditions separately suggests that an increase in the number of cloudy days was to a significant extent responsible for these features. A daily weather type classification based on pressure, pressure tendency, and wind direction shows extremely anomalous frequencies in summer 1816, with only one day (compared to 20 in an average summer) classified as high-pressure situation but a tripling of low-pressure situations. The afternoon temperature anomalies expected from only a change in weather types was much stronger negative in summer 1816 than in any other year. For precipitation, our analysis shows that the 80% increase in summer precipitation compared to the reference period can be explained by 80% increase in the frequency of precipitation, while no change could be found neither in the average intensity of precipitation nor in the frequency distribution of extreme precipitation. In all, the analysis shows that the regional circulation and local cloud cover played a dominant role. It also shows that the summer of 1816 was an example of extreme climate, not extreme weather.

Temperature dependence of global precipitation extremes

Data from the Global Precipitation Climatology Project (GPCP) covering the period 1979–2007 are examined for changes of precipitation extremes as a function of global mean temperature by using a new method which focuses on interannual differences rather than time series. We find that the top 10% bin of precipitation intensity increases by about 95% for each degree Kelvin (K) increase in global mean temperature, while 30%–60% bins decrease by about 20% K−1. The global average precipitation intensity increases by about 23% K−1, substantially greater than the increase of about 7% K−1 in atmospheric water‐holding capacity estimated by the Clausius‐Clapeyron equation. The large increase of precipitation intensity is qualitatively consistent with the hypothesis that the precipitation intensity should increase by more than 7% K−1 because of the additional latent heat released from the increased moisture. Our results also provide an independent evidence in support for significant increases in the number and/or size of strong global tropical cyclones. However an ensemble of 17 latest generation climate models estimates an increase of only about 2% K−1 in precipitation intensity, about one order of magnitude smaller than our value, suggesting that the risk of extreme precipitation events due to global warming is substantially greater than that estimated by the climate models.

Trends in Precipitation Extremes over Southeast Asia

The authors investigate trends in precipitation extremes using daily precipitation data from Southeast Asian countries during 1950s to 2000s. Number of wet days, defined by a day with at least 1 mm of precipitation, tends to decrease over these countries, while average precipitation intensity of wet days shows an increasing trend. Heavy precipitation indices, which are defined by precipitation amount and percentile, demonstrate that the number of stations with significant upward trend is larger than that with significant downward trend. Heavy precipitation increases in southern Vietnam, northern part of Myanmar, and the Visayas and Luzon Islands in the Philippines, while heavy precipitation decreases in northern Vietnam. Annual maximum number of consecutive dry days decreases in the region where winter monsoon precipitation dominates. Decrease of precipitation event in the dry season is suggested in Myanmar.

Long-term changes to incoming solar energy on the Canadian Prairie

Many regions of the earth experienced a steady decline in solar radiation (global dimming) from the late 1950s to the late 1980s–early 1990s and a steady brightening thereafter. To determine trends in solar energy across the agricultural region of the Canadian Prairie, we analyzed incoming solar radiation, sunshine, and climate data gathered between 1951 and 2005 from 7 locations on the prairies. From the 1950s, there was a decreasing trend in annual average daily incoming solar radiation, no trend in annual average daily sunshine hours, and increasing trends in annual average daily temperature and in the annual number of precipitation/rain events. As well, we found the annual average daily incoming solar radiation decreased as the annual number of precipitation/rain events increased, but increased as the annual average precipitation intensity increased. We found the annual average daily sunshine hours decreased as the annual precipitation amount increased and as the annual average precipitation intensity increased. Thus, incoming solar radiation and sunshine responded differently to precipitation amount/events. Nevertheless, climate trends coupled with the relationship of solar radiation/sunshine to precipitation amount/events suggested that increased cloudiness played a key role in the extinction of solar radiation by the atmosphere over the past 50–60 years on the Canadian Prairie. Increasing greenhouse gas concentrations act to reduce cloudiness, whereas increasing aerosol concentrations often increase cloudiness. Specific to the Canadian Prairie, further research is needed to determine the influence of changing greenhouse gas and aerosol concentrations on cloudiness and cloud characteristics and the impact these changes would have on solar energy measured at the earth's surface.

Trends in Middle East climate extreme indices from 1950 to 2003

A climate change workshop for the Middle East brought together scientists and data for the region to produce the first area‐wide analysis of climate extremes for the region. This paper reports trends in extreme precipitation and temperature indices that were computed during the workshop and additional indices data that became available after the workshop. Trends in these indices were examined for 1950–2003 at 52 stations covering 15 countries, including Armenia, Azerbaijan, Bahrain, Cyprus, Georgia, Iran, Iraq, Israel, Jordan, Kuwait, Oman, Qatar, Saudi Arabia, Syria, and Turkey. Results indicate that there have been statistically significant, spatially coherent trends in temperature indices that are related to temperature increases in the region. Significant, increasing trends have been found in the annual maximum of daily maximum and minimum temperature, the annual minimum of daily maximum and minimum temperature, the number of summer nights, and the number of days where daily temperature has exceeded its 90th percentile. Significant negative trends have been found in the number of days when daily temperature is below its 10th percentile and daily temperature range. Trends in precipitation indices, including the number of days with precipitation, the average precipitation intensity, and maximum daily precipitation events, are weak in general and do not show spatial coherence. The workshop attendees have generously made the indices data available for the international research community.

The wind-induced loss of thunderstorm precipitation measurements

Paired elevated and ground level recording precipitation gauges of the electronic weighing type with a resolution of 0.01 mm/min were tested during the 3-year field experiments at two sites in Slovakia. The wind-induced loss, defined as the difference between the ground level and the elevated gauge measurements, is related to the average wind speed and the average intensity of precipitation during a particular time interval. Two intervals of 15 and 60 min of total number of 1611 and 736 precipitation events, respectively, were used in the analysis. The events are divided according to the type of clouds into two groups. The cumuliform cloud group is representative for heavy (convective) precipitation and the stratiform cloud group for all other types of (non-convective) precipitation. The results show a non-linear dependence of the wind-induced loss on intensity of precipitation and wind speed. The wind-induced losses are smaller for the convective precipitation as compared with the non-convective precipitation. There are also differences between the results for the two time intervals. The smaller interval shows larger wind-induced losses than the greater one. The results agree well with the previous findings of the authors and these obtained by the numerical simulation. Using a threshold value of precipitation intensity i ≤ 8 mm h −1 instead of the cloud genesis to separate the non-convective precipitation from the convective one resulted in different wind-induced losses for the group of so defined “non-convective” precipitation. The wind-induced losses differ by up to ± 15%.

Trends in indices for extremes in daily temperature and precipitation in central and western Europe, 1901-99

We analyse 20th century trends in six indices for precipitation extremes and four indices for temperature extremes, calculated from daily observational data for European stations. The indices chosen reflect rather moderate extremes. Most of the ~80 stations used are situated in central and western Europe; therefore, results mainly refer to this region. Trends are calculated over 1901-99, 1921-99, 1901-50 and 1946-99. Two different trend estimators are used, and significance is assessed with a bootstrap technique. We find that: • Significant incr easing precipitation trends over the 20th century dominate in winter for both average precipitation intensity and moderately strong events. Simultaneously, the length of dry spells generally increased insignificantly. • There are few significant trends of any sign for precipitation indices in summer, but there are insignificant drying trends over Scandinavia and wetting trends over central and western Europe for 1921-99. The length of dry spells in summer generally increased insignificantly. • Both the warm and cold tails of the temperature distribution in winter warmed over the entire 20th century. Notably low values in the cold tail for daily Tmax and Tmin occurred in the early 1940s, leading to strong but insignificant negative trends for 1901-50, whereas little change occurred before 1940. • Warming of winters during 1946-99 occurred in both the warm and cold tails for both Tmax and Tmin, with the largest warming in the cold tail for Tmin. • The warm tail of daily Tmin (and to a smaller extent Tmax) in summer warmed significantly during the past century. There is more evidence for summer warming in the first half of the century compared with the second half. • During 1946-99, the warm tail of daily Tmax in summer was generally warming while the cold tail was cooling (both insignificantly). • More digitized daily observational data from various European sub-regions are needed to permit a spatially more extensive analysis of changes in climate extremes over the last century.

A study of the relationship between cloud-to-ground lightning and precipitation in the convective weather system in China

Abstract. In this paper, the correlation between cloud-to-ground (CG) lightning and precipitation has been studied by making use of the data from weather radar, meteorological soundings, and a lightning location system that includes three direction finders about 40 km apart from each other in the Pingliang area of east Gansu province in P. R. China. We have studied the convective systems that developed during two cold front processes passing over the observation area, and found that the CG lightning can be an important factor in the precipitation estimation. The regression equation between the average precipitation intensity (R) and the number of CG lightning flashes (L) in the main precipitation period is R = 1.69 ln (L) - 0.27, and the correlation coefficient r is 0.86. The CG lightning flash rate can be used as an indicator of the formation and development of the convective weather system. Another more exhaustive precipitation estimation method has been developed by analyzing the temporal and spatial distributions of the precipitation relative to the location of the CG lightning flashes. Precipitation calculated from the CG lightning flashes is very useful, especially in regions with inadequate radar cover.Key words. Meteorology and atmospheric dynamics (atmospheric electricity; lightning; precipitation)