验证大气预测模式的实用性

在对鹿泉市市区内的污染源进行调查的基础上，总结出污染物的排放源强。根据全市的气象资料和混合层高度，利用两种方法对鹿泉市市区的污染因子二氧化硫的长期浓度进行估算，并把计算浓度和常规监测浓度进行比较，做误差分析，最后讨论了两种计算方法的特点及在鹿泉市大气环境预测中的实用性     

Early growing season weather variation,expectation formation and agricultural land allocation decisions in Ethiopia

Using unique crop-specific data gathered over 7 years, we study if and how maize-producing farmers in Ethiopia adjust their land allocation decisions in response to pre-planting-season weather variations. We show that farmers adjust their land allocation decisions in response to increased temperatures early in the growing season. In addition to quantifying a substantial adaptation margin that has not been documented before, our study also reveals the presence of a weather variation-induced expansion of maize production into areas that are less suitable for maize cultivation.     

Distributional heterogeneity in climate change impacts and adaptation: Evidence from Indian agriculture

This study estimates the distributional heterogeneity in the effects of climate change on yields of three major cereal crops: rice, maize, and wheat in India using district-level information for the period 1966–2015. We distinguish between the effects of changes in growing season weather from those due to changes in long-term climate trends and the heterogeneity in these effects across the distribution of crop yields by estimating naïve and climate penalty inclusive models using fixed-effect quantile panel models. We observe an absence of adaptation against rising temperatures for rice and wheat. However, we find a statistically significant presence of adaptation for wheat and maize for changes in precipitation, though the magnitude is small. Moreover, we find that the effects are asymmetric, and are larger at the lower tail of productivity distribution and smaller at the upper tail of the distribution. A 1°C increase in temperature lowers rice and wheat productivity by 23% and 9%, respectively at the first quantile, but the damage is only 6% and 5% at the ninth quantile. Heterogeneity in impacts and adaptation estimates over the yield distribution curve and across crops suggests the importance of customizing strategies for adaptation to changing weather and climate conditions across regions, crops, and current productivity levels.     

Agricultural input subsidies,extension services,and farm labour productivity nexus: Evidence from maize farmers in Tanzania

This paper examines the effect of agricultural input subsidies (AIS) and agricultural extension services (AES) on farm labour productivity in plots planted with maize in Tanzania, using panel data from the National Panel Survey in Tanzania. To control for the endogeneity of the two programmes, a control function and instrumental variable approach is used to estimate the effects of AIS and AES on farm labour productivity. The results show that AIS and AES are significant in raising labour productivity in maize-planted plots. Similarly, AIS and AES are also effective in increasing land productivity in these plots. Moreover, each programme has comparable effects on land productivity and farm labour productivity. These findings imply that public investments in AIS and AES are effective in raising farm productivity.     

Mismeasurement and efficiency estimates: Evidence from smallholder survey data in Africa

Smallholder agriculture in sub-Saharan Africa is commonly characterised by high levels of technical inefficiency. However, much of this characterisation relies on self-reported input and production data, which are prone to systematic measurement error. We show theoretically that non-classical measurement error introduces multiple identification challenges and sources of bias in estimating smallholders' technical inefficiency. We then empirically examine the implications of measurement error for the estimation of technical inefficiency using smallholder farm survey data from Ethiopia, Malawi, Nigeria and Tanzania. We find that measurement error in agricultural input and production data leads to a substantial upward bias in technical inefficiency estimates (by up to 85% for some farmers). Our results suggest that existing estimates of technical efficiency in sub-Saharan Africa may be severe underestimates of smallholders' actual efficiency and what is commonly attributed to farmer inefficiency may be an artefact of mismeasurement in agricultural data. Our results raise questions about the received wisdom on African smallholders' production efficiency and prior estimates of the productivity of agricultural inputs. Improving the measurement of agricultural data can improve our understanding of smallholders' production efficiencies and improve the targeting of productivity-enhancing technologies.     

Linkages between natural gas,fertiliser and cereal prices: A note

We use structural vector autoregressions to analyse the dynamic effects of shocks to natural gas and nitrogenous fertiliser prices on three major cereal crops: maize, rice and wheat. We find that the response of cereal prices to natural gas and fertiliser price shocks has been relatively small, instantaneous and transitory. These findings suggest that crop prices may change rapidly in response to energy and fertiliser prices, even when there are no shifts in the underlying fundamentals in crop markets. Furthermore, because the effects of the shocks dissipate rather quickly, short-term measures to address swings in food prices may suffice.     

Delayed monsoon,irrigation and crop yields

Most of the empirical literature assessing the impacts of climate change on agriculture has modeled crop yields as a function of the levels or deviations in the growing-period rainfall. However, an aspect that has received little attention in the empirical literature relates to the relationship between the timing of monsoon rains and crop yields. Using a pan-India district-level panel dataset for 50 years, this article investigates two interrelated issues critical to understanding the impacts of weather-induced agricultural risks and their management. It first examines the impact of the timing of monsoon onset on crop yields and then assesses the role of irrigation in mitigating its effects. The article finds that the delayed onset of monsoon is detrimental to crops, and its effects are realized beyond the rainy season. The findings also demonstrate that irrigation helps mitigate the harmful effects of delayed monsoon. Finally, to link these findings to farm-level adjustments, the article shows that farmers explicitly adjust the timing of irrigation in response to delays in monsoon rains.     

Effet du changement climatique sur la production vivriere au Togo

This paper analyzes the effects of climatic variables on food crop yields at the prefectural level from 1996 to 2016 in Togo. Using the panel-corrected standard errors method and panel data from departments in charge of agricultural statistics and meteorology, the results show that meteorological variables have various effects on food crops yields, but the negative effects are dominant. In addition, adaptation strategies through agricultural land reallocation have not enabled farmers to improve food crops yields. There is an urgent need for public authorities to implement actions to strengthen farmers’ resilience through practice adoption and cultural innovations for adaptation to climate change.     

The roles of risk preferences,selection, and uncertain returns on land contracts

Using panel data on a statistically representative sample of Iowa farmland parcels from 1997 to 2017, we analyze the factors determining whether land is farmed by the owner or rented out under a cash rent or crop share contract. The landowner's decision to rent or operate the land depends on the distribution of expected net returns to the land, and so estimates of the factors affecting rental terms will be biased if the sample only includes rental contracts and excludes the owner-operator. Land with higher mean and/or lower variance of expected net returns is most likely to be rented out. Participants in the rental market will include the most risk-averse landowners and the least risk-averse tenants, while the least risk-averse landowners operate their own land. Our empirical results suggest that the rising use of cash rent contracts and declining incidence of owner-operation and crop-share rental contracts is consistent with falling coefficient of variation in expected net returns per acre.